You can run a repair on the versions, sequentially, oldest, first. No lasting harm done. However, straighten out the separate files first and do the registry hack. Then do the repair, doing the one for your default go-to version last.
Repair an Office application - Office Support

For your older versions, you will need your installation media and possibly your product key for the repair.

I do have an Office 2003 installation CD with a registration key. But when I put it in the DVD drive on my refurbished PC, it made an infernal racket, like the engine room of a tramp steamer, like this:

Flickr

It went on like that for quite a while, but thankfully it finally stopped on its own. I was afraid to hit the eject button on the drive out of fear that I would disrupt whatever it was trying to do.

But after the racket subsided, and I restarted my PC, I could find no evidence of any installation process.

I thought the drive might be faulty, (I hadn't thought to test it when I received the refurbished PC), so I inserted a music CD, and it played fine. (Well, not quite fine, it did make a bit of a clunking sound when I clicked the advance to the next track button on the player app).

So, I'm going to hunt around on the web for Office 2003 installation instructions. I thought all I would have to do was simply put the CD into the drive and it would automatically start the installation process.

These things take me a lot of time these days. I have difficulty sitting up at my PC for more than a few minutes at a time, due to worsening chronic health issues. So if I don't post for a day or two, don't take that to mean that I've abandoned this project. I really do need to get my "new" PC up and running so I can pull the plugs on my old XP and Windows 7 PCs.