It is only the view of Shaivas, Vaisnavas etc.. who think Lord Brahma is a post and one can achieve it by doing Karmas/Yajnas.
For the Hiranyagarbhas; Lord Brahma is the ultimate reality and is the Lord of the all. So, he is not post but he is Supreme Lord.
In the Brihadaranyaka Upanishad Vartika (3.7) Sureshwaracharya, who is direct disciple of Adi Shankaracharya writes:
यः पृथिव्यामितीशोऽसावन्तर्यामी जगद्गुरु ।
हरिर्ब्रह्मा पिनाकीति बहुधैकोऽपि गीयते ।।
He who is residing inside the prithivi devata but whom prithivi devata doesn't know is said to be Antaryami and is the teacher of the universe. That Antaryami has been sung as Hari, Brahma and Pinaki (Shiva) and many.
From the above quote it is clear that during the time of Sureshwaracharya too there were Hiranayagarbhas who hold Lord Brahma as the Antaryami of all (and not as post/position).
In this chapter of Mahabharata too Lord Brahma is told to be unmanifest, and declared as unborn:
तथा प्रजापतिर्ब्रह्मा अव्यक्तः प्रभुरव्ययः।
येनेदं निखिलं विश्वं जनितं स्थावरं चरम्॥
अण्डजातं तु ब्रह्माणं केचिदिच्छन्त्यपण्डिताः।
अण्डाद्भिन्नाद्बभुः शैला दिशोऽम्भः पृथिवी दिवम्॥
द्रष्टव्यं नैतदेवं हि कथं जायेदजो हि सः।
स्मृतमाकाशमण्डं तु तस्माज्जातः पितामहः॥
The Lord of all creatures, Brahma, unmanifest, endued with puissance, and of unfading glory, who created this boundless universe with its mobile and immobile creatures (is a Brahman). Some persons there are, destitute of wisdom, who say that Brahma was born of an Egg. From the original Egg, when it burst forth, mountains and the points of the compass and the waters and the earth and the heavens all sprang forth into existence. This birth of the creation was not seen by any one. How then can Brahma be said to have taken his birth from the original Egg, when especially he is declared as Unborn? It is said that vast uncreate Space is the original Egg. It was from this uncreate Space that the Grandsire was born.
One of the important quote in the above passage is "How then can Brahman be said to have taken his birth from the original Egg, when especially he is declared as Unborn?"
But where is Lord Brahma declared to be unborn? Actually it is in the Vedas itself Lord Brahma is declared as unborn; ie. As self existent. I discuss it in my answer here and quote is from Shatapatha Brahmana of Yajurveda:
- Verily, Pragâpati alone was here in the beginning. He desired, 'May I exist, may I reproduce myself!' He toiled, he practised austerity (or, became heated). From him, worn out and heated, the waters were created: from that heated Person the waters are born.
The above quote is itself self-explanatory. Not only in Vedas also in many Puranas Lord Brahma is declared as unborn. Actually many people are aware of only Puranas glorifying just Vishnu or Shiva. But there are plenty and plenty of passages in many Puranas which state Lord Brahma is the Lord of all. For eg. 1.4 of Kurma Purana:
He resorts to the special creation, destroys as well, while protecting the same at the same time. Because of the said quality, he is conceived to be one in all the three times, i.e. past, present and nature. The eternal Hiranyagarbha Brahma appeared first of all. Because of his emerging on earth, first of all, he has been known as Adideva. Because of his being unborn, he is also called as Aja. All the people are maintained by him because of which he is also known as Prajapati. (Kurma Purana 1.4)
Now, again there are many objectors who claim that Lord Brahma is born. He takes birth from lotus navel of Vishnu etc.. etc.. First of all the view of Brahma coming from navel of Vishnu is not mentioned in Vedas at all, it is only view of Puranas and some parts of Mahabharata. Even Vasistha when gives description about creation of Universe in Ayodhya Kanda starts from mentioning of Lord Brahma.
And secondly Brahma taking birth from Vishnu is just stated to be act of Brahma itself in Puranas. For eg. In Kurma Purana (1.9) it is told that Brahma enters stomach of Vishnu and emerges from navel of Vishnu and thus giving his name Padmayoni. So, it is not his real birth at all.
Again there are some things like life if Brahma being age of 100 yrs. etc.. etc.. It is all thing which is planned by Lord Brahma himself for the purpose of manifestation of creation. It his only his pretence. It is made clear itself in Vishnu Purana:
PARÁŚARA.--The essential properties of existent things are objects of observation, of which no foreknowledge is attainable; and creation, and hundreds of properties, belong to Brahma, as inseparable parts of his essence, as heat, oh chief of sages, is inherent in fire. Hear then how the deity Náráyána, in the person of Brahmá, the great parent of the world, created all existent things. Brahmá is said to be born: a familiar phrase, to signify his manifestation; and, as the peculiar measure of his presence, a hundred of his years is said to constitute his life: that period is also called Param, and the half of it, Parárddham. I have already declared to you, oh sinless Brahman, that Time is a form of Vishńu: hear now how it is applied to measure the duration of Brahmá, and of all other sentient beings, as well as of those which are unconscious, as the mountains, oceans, and the like. (Vishnu Purana 1.3)
So, it is clear from above passage when it is said that Brahma is born it is said just to signify his presence.
The actual Sanskrit verse used in that passage of Vishnu Purana is as:
निजेन तस्य मानेन आयुर्वर्षशतं स्मृतम् ।
As a result of this pretence he is said to have age of 100 years.
So, it is clear that Lord Brahma is not a post he is Lord.
For the passages like 'Brahma is Jeeva' we can say 'As Lord Brahma is everything, so yes he is also a Jeeva.' For the various episodes like Lord Brahma being cursed or similar things like this, these are just Leelas of Lord Brahma.
Regarding the views of Shaivas, Vaisnavas etc.. they would have their own interpretations of the quoted passages (obviously). And they may also have rituals, statements etc.. for attaining position of Brahma. But I'm answering the question not by giving rituals to get post of Brahma but by showing that 'Lord Brahma is not post at all.'