ok so i know all the modes of Gmaj
so if i wanted to play in Amaj, could i just play all the same scales 2 frets higher?

Yes. That is exactly how it works.

But that's not modes. It's just the different major scale patterns over the fretboard.
Indeed, you just move the scale shapes up 2 frets.

But be advised, that you're not playing in 7 different "modes" in G Major, but you're just using 7 different shapes all over the fretboard that are all in G Major (or the G Ionian mode). Playing different modes of the G Major scale is something else, something more complex.
If you're playing the A Dorian scale shape over G Major, you're still playing in G Major. If you play the chords of G Major in a way that they resolve to the A Dorian (i.e. Am - D7 vamp), then you're playing in A Dorian.