Is there any method to clear Bramhahatya(Killing a Bramhana) Sin other than Ashwamedha Yagna?. Since Ashwamedha Involves being king and sacrificing horse which is violent method, and must be avoided if we can.
There are many methods to remove Brahmahatya Sin and visiting Kasi (Varanasi) is one among them. This is described in Chapter 182 - Mahatmya of Kasi Tirtha of Matsya Purana.
आदेहपतनाद्यावत् क्षेत्रं यो न विमुंचति।
न केवलं ब्रह्महत्या प्राकृता च निवर्त्तते।। १६ ।।
प्राप्य विश्वेश्वरं देवं न सा भूयोऽभिजायते।
अनन्यमानसो भूत्वा योऽविमुक्तं न मुंचति।। १७॥
तस्य देव: सदा तुष्टः सर्वान् कामान् प्रयच्छति।
द्वारं यत्सांख्ययोगानां स तत्र वसति प्रभुः।। १८ ।।
One who goes there anytime is purified of the sin of even killing a Brähmana. One who continually resides there, for all his life, unmoved in mind, is not only purified of his sin committed in this life, but also of his Brahmahatyā sin in his previous birth, and attains Visveswara (Siva) and does not get any other births. He gets the favour of Siva and all his desire are fulfilled, and he gets the same end as the knower of Sāmkhya does. He remains there all his lives and never quits it.
In Mahabharata, Anushashan Parva, SECTION XXV, Yudhishthira has asked to Bhishma about the greatness of sacred waters. In this context Bhishma told the story in which Sage Angiras has described the greatness of sacred waters to Gautama. According to Sage Angiras bathing in some sacred waters one can be freed from the sin of Brahmanicide.
By bathing, after a fast of three days and purifying the mind of all evil passions, in the large lake of Bhrigu Kunda, one becomes cleansed of even the sin of Brahmanicide.
Bathing in Asmaprishtha and Niravinda mountains and Kraunchapadi,--all three in Gaya--one becomes cleansed of the sin of Brahmanicide. A bath in the first place cleanses one of a single Brahmanicide; a bath in the second cleanses one of two offences of that character; and a bath in the third cleanses one of three such offences.
Repairing to Indratoya in the vicinity of the mountains of Gandhamadana and next to Karatoya in the country called Kuranga, one should observe a fast for three days and then bathe in those sacred waters with a concentrated heart and pure body. By doing this, one is sure to acquire the merit of a Horse-sacrifice.
Bathing in Ganga hrada and the tirtha known by the name of Utpalavana and daily offering oblations of water there for a full month to the Pitris, one acquires the merit of a Horse-sacrifice.
Bathing in the confluence of the Ganga and the Yamuna as also at the tirtha in the Kalanjara mountains and offering every day oblations of water to the Pitris for a full month, one acquires the merit that attaches to ten Horse-sacrifices.
Bathing in Utpataka and then in Ashtavakra and offering oblations of water to the Pitris every day for twelve days in succession, abstaining the while from food, one acquires the merits of a Horse-sacrifice.
Observing a fast for three days and bathing in the tirtha known as Kulya and reciting the sacred mantras that go by the name of Aghamarshana, one attains the merit of a horse-sacrifice.