Just a thought- This is good (in my opinion).
Do nothing. Leave everything EXACTLY as is.
Call him on his cell phone. Today. Tell him you found a few minor things that needed some improving. Tell him with the help of your friends here at APS, you made some minor changes, and you think they are for the better. Tell him they are so minor it may take him a little bit to figure out what they are.
Then laugh a little and hang up.
Then leave a note on his door when he gets home, welcoming him home.
Sign it "The APS redecorating committee".
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Changing stuff in his house will get one or two days worth of reaction out of him.
This will make him think all week, and make him spend weeks afterwards trying to firgure out what you did.