Does the egg pool change for Community day?

I don't think egg pools have ever changed for a community day. The only one that had any impact on eggs was the April Mareep day when distance was cut to a quarter of the usual, but no change in the actual eggs themselves.

So yeah, probably still the same 2K water festival eggs.

Technically no.

Realistically... who knows? During the Mareep Community Day I got a 10km egg and hatched a Mareep from it. A 100% Mareep, yes, but it was like I was living in an Xzihibit meme. "Yo Dawg, I heard you were having a Mareep day, so I put a Mareep into a 10km egg on your Mareep Day!"

(worst of all? it hatched AFTER the event, so I couldn't evolve it to an Amphrose with the special move. Sigh!)