Basically as long as you aren't making 'structural changes' then it's all good. Rugs, curtains, hanging picture on existing hooks are all good.

So yes to the curtains -just make sure the red ones are on the entry report so they don't think you are taking off with the good curatins Installing blinds is out. Installing anything is out without approval. You'll need approval to put hooks and things in the walls. No harm in asking though