Can you go to meps and pass thru with the guard then change to active duty at meps ?

No it doesn't work like that. The MEPS is just a place where people are screened. If you want to be on active duty you need to contact an active duty recruiter

I'm not sure why you'd want to?
Until you've signed a contract, you can essentially attempt anything you'd like, but once you've put pen to paper then you're committed to that path and nothing else is guaranteed.

Honestly though, if you want to be active duty, then you should simply pursue that openly and from the get-go.