Coordinates are Cartesian coordinates referenced to the centerpoint of the model. You know, x/y/z. It works the usual way a Cartesian coordinate system works. Type in new numbers to move it around etc etc.
(Or rather, in PCS2 it's -x,y,z wrt. the FSO engine but don't worry about this except for fvec/uvec and if you're trying to use PCS2 to reference nebula trail origins on a non-symmetric model.)
You don't swap textures. You edit the texture, because you don't work with
****ING TILEMAPS, okay? But to rename textures simply select the texture from the texture list on the left hand side panel, then change the name in the right hand side panel.
