use ang_add to change a temp vector, then set your player position vector to it for object axis oriented rotation:
if(key_g==on){vec_add(temp.x,(1,0,0)}
ang_add(temp.x,player.x)
vec_set(player.x,temp.x)

or you can adjust your angles with sines and cosines, vec_for_angle, and vec_to_angle which might work depending on your situation. Oh yeah, my game that has an angel flying around wouldn't work if you couldn't rotate him whichever way you want. I've found that 3D gamestudio's "Euler" rotation allows pan to only rotate around the z, tilt to rotate around x or y and roll around any axis (now that's pretty confusing!)