The tag name belt-driven-chains is oxymoronic: a belt is not a chain!
It makes sense to me to merge it with the simpler and more accurate belt-drive.
Can this be done? How?
Yes, we can do this. How is to post on meta (like you just did), wait for people to have a chance to comment on your proposal, then one of the moderators makes it happen.
There's also a method that high-rep users can use to create a tag synonym, but we really don't have enough users with the rep, so a meta post and moderator intervention is the way to go.
I looked at it, and somehow the synonym was backwards with everything being automatically rewritten as belt-driven-chains. I reversed the synonym and merged the tags so that everything is belt-drive now.