As I understand it, Mover 5 will automaticlly update changes you make to imported Poser files (such as changing position or posing) when you reopen a file in Vue. Does that mean that if I make changes to the texture in Vue, this will be overwritten? Or will it only update the changes I make in Poser, and leave the textures already in Vue alone.

If this is Vue Pro, it will prompt you to update the file (which will re-import the object) and if you say "yes" to update, it will then prompt you on whether or not you want to update the textures that are currently applied to the model (but only if you have changed them in vue.) This also applies to other file formats as well, as long as the file you edit in the other program has the same name and location as what you have imported into Vue 4 Pro. Hope this is what you were looking for.