"Creative changes" to initial Eidolon

[Raviel_Incarnate]

So I've been playing for a couple weeks now, and as I'm getting more acquainted with the game, I've come across the summoner class. Immediately I printed out a sheet for it and decided to go dual snake, using my Nagaji boon alongside a serpentine base form eidolon. HOWEVER. I want to make a Lamia-shaped eidolon, and as much fun as it might be to imagine her swallowing an enemy whole.... It doesn't make much sense to have a bite attack, or reach on said bite. So...

Is it (arguably) allowed for me to switch the reach from bite to tail slap, and lose bite and climb for arms (that don't really do anything at this point)?

[Starglim]

You can change all of the eidolon's evolutions (but not its base form) at each level.

[Raviel_Incarnate]

The base form is actually what I want to change. A lamia ALMOST fits, but that bite makes no sense. Lamia have a human torso, so a bite would be pretty weak.

As an additional question, can I say my eidolon has arms for the sake of RP without the limbs evolution?

[El Baron de los Banditos]

The issue here is that it's PFS. Changing the base form won't be allowed, but the arms (as long as you're not getting a mechanical benefit), you might be able to describe it that way. I'd say "Expect table variation," 'cause that's the safest answer.

[Serum]

Well, everything you want to do with the base form is illegal in terms of RAW, so you'll have to talk to your DM about it.

You can say your eidolon has arms, but the arms will be completely non-functional (unable to even hold items).

You can just not use the evolutions and pretend they aren't there.

[Raviel_Incarnate]

Welp... I guess I'll HAVE to do that. For the "legal" version, which I made first, I just gave her arms and reach on tail slap. Thanks everyone.

Btw, I have not yet named my actual character, though my lamia has been dubbed Alipheese (Alice for short)

Any suggestions? Naga-blooded Male