Is it possible to do a visa run at Mae Sai border if I have a METV next month?

you wouldn't be doing a visa run <- that's where you go to a thai consulate and BUY a visa

You'd be doing a 'border-bounce' <- that's where you go to the border, stamp out of thailand, stamp in&out of another country and then stamp back into thailand to get either a visa exempt entry or to activate another entry on a multi-entry visa.

Yes you can go there to border bounce and activate another 60 day entry on your visa