If I change my gamer name to something else will previous heads i lost or farmed be effected also?
A player head is a skull, linked to the current texture of a certain player in Minecraft. You can use those heads in any Minecraft version. Since the skull is linked to a player, it will change the texture if the player changes his texture. If the player changes his username, a newly created player head with his name will have no texture.
Sounds like the name of the head won't change but if the texture changes, it will also change on the head.