I have a shaded area in the front of my house. The area is filled with a beautiful moss. They neighbors pooch has peed there a few times and it has yellowed. Is it better to leave the yellowed moss and let it come back (will it?) or should I clear the yellowed bits out and let the moss retake the area?
The moss will almost certainly come back, but you can probably move things along by flushing the area with water to dilute / transport the salts.
So just a hose on shower on it for a bit each day? Also if I were to add some variant mosses into the volunteer would they just compete to much to make it worth it to try?
Yes, just to disperse the salts. Mosses seem to be at least as picky as other plants when it comes to establishing in areas, so you'll have to look for different species that are enjoying a similar habitat if you want to introduce diversity. At the least, you'll need something that grows under a similar light and watering regime in pretty much the exact same soils.