Larry,
I have renamed and renumbered hundreds of files using the keyboard (very slow), using windows Explorer or using a renaming/renumbering program such as CKRename. I have had absolutely no problems with any of the methods.
Just remember, you can not have more than one file starting with the same number. If you do, only the first file will be read. The second one will be invisible to the KN7000.
You said:
"After doing this, number 15 will show up on the 7000, but may not load, sometimes a message no file on 15 appears on the 7000 screen. However if I go into Disk Tools and hit the Delete button for 15, magically 15 is fixed and loads and plays."

Is it possible that there already was a file on 15, but without a name? If so, this would explain the whole thing. When you went to Disk Tools and deleted 15, you removed the un-named file which allowed the KN7000 to read the desired file.

I would strongly recomend using the program CKRename. It was recommended by Technics Player some time ago, is free, and works like a charm.
Go to: http://www.musicsucks.com/CKSoft/CKRename/

I think that you will like it.
Regards
Walt