The piano sits on the ground floor, but both residentials and guests are obsessed with playing it, which results in neglecting their bladder/hunger/energy needs if I don't cancel the action. I've also placed a guitar in the basement, but the Sims are less likely to play with it.

Not what you're asking for, but you can stop visitors from using your music instruments, with Pescado's no buskers and Neder's Visitors, stay off my stuff.

I don't know if there's a mod that makes the piano less attractive, in my experience those hacks can only do so much because how much an object attracts the sims depends on what else there is on the lot that they consider attractive.

What you can do is move the piano: sims don't care on what floor an object is, but they do consider the distance. The further from the road/entrance, the less attractive... provided there is something else for them to do closer.