I'm asking from all four part of Vedas, was Indra ever changed?
To answer this question it is required to know the basics of the teaching of Vedanta properly. Here I'll give an answer according to the Vaishnava systems of Vedanta, specifically from the Gaudiya Vaishnava system.
Vedanta teaches that there are two fundamentally different types of entities or beings. One are independent entities, and the other are dependent entities.
The independent entities are all eternal, namely their position or post is eternal, or if you wish we can say their life is eternal. Their post or life is not temporary, it never stops, it has no an end, they never die! The independent entities, for example, are Lord Vishnu (also known as Narayana) who is known to be Brahman or the Absolute of the Upanishads and his spouse goddess Lakshmi (also known as Sri). We can say they never stop to be God Vishnu and Goddess Lakshmi. They are eternal God and Goddess, they are eternal divine couple.
On the other hand the dependent entities can have either eternal or temporary life or post. The dependent entities are called living beings, jivas or jiva souls (jivatmas), they are different from Brahman, they are not Brahman or the Absolute of the Upanishads. Whether jivatmas' life is eternal or temporary depends on the world where they live. Thus the jivatmas live in two fundamentally distinctive worlds with their distinctive natures, namely the material world and spiritual world often called Vaikuntha or World of Brahman.
All the living beings in this material world whether they are plants, insects, animals, humans or the devas (gods) in heaven are the dependent entities, they are all jiva souls (jivatmas). All jivatmas in this material world have a temporary or transient post or life. Even a great devas (gods) in heaven are all temporary or transient, and their lives have a limited duration of time. This includes even the most important devas such as Brahma (the god creator), Shiva (also known as Rudra, the god destroyer), Indra (the king of heaven), Agni (god of fire), Vayu (god of wind), Surya (god of the sun), etc, they are all temporary gods with limited duration of life. They are all jivatmas with temporary or transient posts and life. They are not eternal gods, however they are eternal only in the sense that their soul or jivatma is eternal, but as soon as they die their soul has to be embodied again in the new body and thus they acquire new post or life.
On the other hand the jivatmas living in Vaikuntha or World of Brahman are all liberated souls with eternal life, namely their life or post does not change, they all live eternally, they never die.
Thus all jivatmas living in this material existence including devas Brahma, Shiva (Rudra), Indra, Agni, etc, are dependent entities and their characteristics are:
a) First of all they are dependent, and what "dependent" means is that their life depends on some other God who is superior to them and who governs their life and also sustains their life, namely that God provides them with power and everything they need for living. That God who is superior to them and who governs and sustains their life is Lord Vishnu, and it is also goddess Lakshmi. On the other hand Lord Vishnu and goddess Lakshmi are independent which means that their life does not depend and is not governed by some other God. Their life is completely under their own control and decision.
b) Since they are dependent they have to abide by the laws of Lord Vishnu, and they are responsible according to those laws, they have karma which is one of those laws and thus they are responsible for their actions or deeds. This point b) follows directly from the previous one, point a) above.
c) Since they are susceptible to the laws and karma specifically, they have merits and demerits, they have a temporary material body which is awarded to them according to their karma and thus their status is limited in all possible ways, namely they are subject to death, their life is limited in time, they are limited in abilities and power as well, they are bound in this world and hence they have to seek for liberation or moksha just like any other jivatma in material existence. They can get moksha if they become self-realized souls, ie if they realize Brahman.
I think that in Sruti for all devas Brahma, Shiva (Rudra), Indra, Agni, etc, at least some of those points are mentioned if not all the points with all their specifics and details. Now, specifically just for Indra there are some verses in Sruti that cover some of the points. I do not know many of them though, but here are those regarding his temporary post or status:
1) The Brihadaranyaka Upanishad 1.4.11-12 says:
- Verily in the beginning this was Brahman, one only. That being one, was not strong enough. It created still further the most excellent Kshatra (power), viz. those Kshatras (powers) among the Devas,-- Indra, Varuna, Soma, Rudra, Parjanya, Yama, Mrityu, Isana. ...
- He was not strong enough. He created the Vis (people), the classes of Devas which in their different orders are called Vasus, Rudras, Adityas, Visve Devas, Maruts.
The verses say that at the beginning of the creation the only being who existed then was Brahman, and he created various gods including Indra. It tells us that all these gods are temporary, they are not eternal because they did not exist at the beginning at all.
2) The Narayana Upanishad of Krishna-Yajurveda says:
nārāyaṇād brahma jāyate | nārāyaṇād rudro jāyate | nārāyaṇād indro jāyate | nārāyaṇāt prajāpatayaḥ prajāyante | nārāyaṇād dvādaśādityā rudrā vasavas sarvāṇi ca chandāguṃsi | nārāyaṇād eva samutpadyante | nārāyaṇe pravartante | nārāyaṇe pralīyante | etad ṛg veda śiro'dhite || oṃ atha nityo nārāyaṇaḥ |
From Narayana emanates Brahma. From Narayana emanates Rudra. From Narayana emanates Indra. From Narayana emanate the Prajapatis (The Divine Progenitors). From Narayana emanates the twelve Adityas, Rudras, Vasus and all the Vedic metres (chandas). From Narayana only do they proceed. Through Narayana do they prosper. In Narayana are they reabsorbed. This is taught as the head of the Rig Veda. Narayana is eternal.
From these verses we see that Indra, as well as other gods such as Brahma, Rudra, Prajapatis, Adityas, Rudras and Vasus, originate from Narayana. So at first the only Lord who existed was Narayana, who is stated in the last words of the quotation to be eternal God, namely "Narayana is eternal". This tells us that all these gods are temporary, they are not eternal because they were created by Lord Narayana who is stated to be the only eternal god among them. One more thing is important here to notice when it comes about the temporary and transient status of all those gods, it's the verse says nārāyaṇe pralīyante. The word pralīyante (pralī) means "reabsorbed, annihilated, to die, to perish". Thus it means that they will be absorbed back to Narayana who created them at first, and it also means that their material body will be destroyed. In the above Brihadaranyaka Upanishad and Narayana Upanishad verses it is said that they were created or born and in the Narayana Upanishad it is said that they were "reabsorbed, annihilated". All those expressions "created" or "born" (jāyate) and "annihilated, to die, to perish" clearly indicate that all those gods have a material body which has to be born, live limited duration of time, and finally perish. So their life cannot be eternal, they are temporary and transient. And it also tells that they are all dependent beings and not independent, they are subject to the law of karma which clearly means that they are dependent. I explained those things above in points a) to c). They are dependent on Brahman, Lord Narayana, because he awarded them with the body according to their merits or karma, he assigned them their respective posts according to their merits or karma, according to what they deserve. The Narayana Upanishad even says "Through Narayana do they prosper" which also indicate their dependency on Lord Narayana.
There are some other verses in Sruti which also tell that Indra and other devas has a material body. Such verses also indicate that the devas are temporary and transient, as well as dependent beings.