I've already unwrapped everything and painted everything but... pls help

Sorry if this question has been asked before but I’ve already unwrapped everything after I mark seam on every specific edges. I have painted a model and stuff… some of it but then i forgot to add in some object to it. But since I’ve already unwrapped and all, is it too late for me? If i add another object, should i unwrapped that object too but i know it will affect the model I’ve already unwrapped

If you have space between your islands you can try to manually move it there. You can also unwrap the specific part and assign another texture to it. You can also try to create a texture atlas.