OK, I wasn't aware of the fact that I could replace the object's texture and keep it correctly mapped just by calling setTexture(), so sorry to bother you with such trivia.
But since you came up with the problem of replacing textures on objects using multiple textures at once, I'm wondering how you would do so. PolygonManager provides a means to get information about every polygons texturing. This would mean I'd have to iterate through all the polygons of an object, putting them in groups of "same texture" and afterwards changing every single polygon's texture accordingly. Would this be the right way to do it, or are there any other, cleverer strategies?