Pathfinder: Can a summoner alter the appearance of his eidolon?

[Bryan]

The summoner controls the appearance of the eidolon. So can he alter that appearance at will or with each new summoning?

[marphod]

The Eidolon can be rebuilt each level, so they can control it on at least that schedule.

A Summoner with 2nd level spells can use Alter Self on the Eidolon, which will allow per-casting control.

On the other hand

This control is not fine enough to make the eidolon appear like a specific creature.

Implies that the level of control isn't that fine. So probably not without a specific spell or the per-level rebuild.