With some help from Robert at Yamaha (who gave me the 'raw' syntax of the MIDI Tempo command), and things I found at various sites, I found a solution to what I wanted to do here. It was a bit tricky, as MIDI tempo is not as simple as I had hoped it would be! :-)

Thanks to those before me for some of the details about how MIDI Tempo works, some formulas, etc. After a lot of experimentation, I got things to work.
I'm sharing my results via the attached PDF (From Excel) file, which has more details.

I used the syntax give to me by Yamaha for Sys-Ex for MIDI Tempo Control (F0 43 7E 01 t4 t3 t2 t1 F7) (see page 96 of Data List),
and the formulas I found online, then experimented 'til I seemed to get it working OK. Once I got it working, turns out it was easy to
let Excel do the math, and the Decimal-to-Hex conversions for me (via formulas I put in my Excel file.

Even though I talk about Tyros5 here, it's likely this will work for many other Yamaha keyboards too!

I could not attach the actual Excel file (not allowed), so I made a PDF from it. If anyone wants the actual Excel file (with the math / calculations / conversions) I can email it to you.

I hope that this is helpful to someone!
-Jim