I am curious if there is a way to assign pet beds to pets. You can assign beds to sims, and you can assign a preferred sleeping spot for pets, but as far as I know you cannot assign a pet bed to a pet. Is there any way I could make a mod that does this?

Try this: Reservable Pet Bed

Unfortunately, this seems to be a Sims 2 mod.

I don't think this functionality is possible in TS3 without making a new object script. There was some similar discussion about having this for vampire altars and the answer was to swap the script with a regular bed- but pet beds don't have that same luxury of being able to do that.

Always wanted to bbe able to assign altars, but never saw a mod for it. I'll have to try cloning an altar and swapping the scripts in s3pe. ))) Worst to happen is that it doesn't work.

You can also use Transmogrifer to check ingame.
It was discussed over at NRaas recently, but I don't think there was confirmation if it had worked. As long as the altar has the same interaction slot, I suppose it might. The sims will look a little silly pretending to get under a blanket, though.

I have used transmogrifier for a few things... not for the altar/ bed. I am actually waiting for my game to load as I type. After I made the altar clone and opened in S3PE to switch the gameplay object script, and then also thought about animations. I'll post what happens.

Edit: Does not really work. You can assign an altar, but it does use bed animations, and looks silly.