I can't change anything around. What can I do to decorate?

I’m moving in with one of my relatives. She is handicapped and can’t get upstairs anymore, so she is renting the entire upstairs to me. The rooms up there are a master bedroom, a smaller room that has been converted into an office, another small bedroom that will probably be storage, and a bathroom. I can do whatever I want to the bathroom because it is really plain, but the rest of the space has been painstakingly decorated in a very tasteful, understated style,. The master bedroom is painted a really nice lichen green color with a dark brown runner. My personal style is very quirky and I love bright warm colors. I also have a huge collection of art for the walls. So… what are some cheap ways to make this place as “me” as possible, without messing anything up? I really want to be considerate about it.