You cant really take a lot of CC's out of a pentroof designed chamber very easily even with the tools TBH, you can get some out of it, but not enough for big changes in CR.

Dropping from 8.0 to 7.5 will need nearly an extra MM on the gasket.

Squish will indeed be effected, potentially meaning you have to run slightly less timing to avoid det, but i personally doubt it would be an issue on a moderate spec YB, they arent exactly cutting edge design on squish anyway, but i havent tried it personally myself so you need to talk to Stu or Karl really, as i only know it will effect it, but i dont know exactly how much by like they will as know doubt they have both mapped an engine like that at some point.
I would strongly recomend avoiding any off the shelf chip for such an application though and would suggest you get it livemapped by someone like Stu or Karl.