Simple Q&A by RAW for Pathfinder 4

[Crake]

Q21

The summoner eidolon evolution section says "Each eidolon receives a number of evolution points that can be spent to give the eidolon new abilities, powers, and other upgrades. These abilities, called evolutions, can be changed whenever the summoner gains a new level, but they are otherwise set." Does this allow the summoner to change the base form evolutions?

For example, you're trying to emulate a marilith, and go with the serpentine form, but don't want bite, or reach with bite, can you trade those away for arms instead upon levelup?