Only if you have multiple buffs set on the avatar when you first summon it - that is the very first occasion that it is brought out of the avatar pool. Once the initial buffs are set, they cannot be changed other than by building over the existing habitat.
If you have multiple buffs held on the avatar, then you can switch which is active by dismissing and re-summoning it and selecting the new one .
Kera:
Proud leader of Shattered Moon