Hello Oreocreme. Sometimes the modders will put a new mod on an original map so that the only room that changes is the new room, what I call a "stand alone" mod. Other times they mod multiple rooms and upload them as a bundle. Installing mods will replace your current maps and you may end up having mismatched rooms by not installing all of the maps in the bundle. Which bathroom mod are you referring to? Perhaps there's a "stand alone" available somewhere.

Always make sure you have a backup copy of your games original images and of any mods you're using and don't want to lose.