But thinking about all the things you could do and actually doing them are two separate things. You do not need planning permission to change the use of a room in your house and people often change a spare bedroom to a study or vice versa. Turn that extra bedroom into a home movie theater.
Make the desk as inconspicuous as possible by matching it to the rest of the furniture.
Make the desk as inconspicuous as possible by matching it to the rest of the furniture. We have an old house with 3 small rooms and no master. First swap out the study furniture for proper bedroom furniture. You can include storage in the form of open shelves.