Are there code restrictions when adding an access panel in the ceiling below a bathroom?
You can add the access you want in the basement without worries unless your basement is a garage (like a daylight basement). If it is a garage then it would need to meet fire code, but if just an environmental space you could create your access similar to a standard scuttle hole for attic access, but hold it in with a few screws. As far as creating access in the wall of the living room, I have seen some very artistic covers for electrical panels in walls (that do not need tools to open) but could do the same for plumbing access. Think of a picture frame on a hinge that could be opened as a possibility.