CA stimulus is going out for ppl who are 75k and under. I filed married and combined we are over but individually my wife is under. Should/can I amend to be eligible?

you have to prepare it both ways to find out which is more favorable.

No one here can tell you what the outcome will be.

Do you mean to amend to Married filing Separate?  It's too late to change to MFS if you already filed Joint.   But here is a CA page on eligibility.  Scroll down to see MFS and amounts.

https://www.ftb.ca.gov/about-ftb/newsroom/golden-state-stimulus/help.html  

If you file MFS you may end up owing more than you would get for the Stimulus.   So it may not be worth it.