It worked!

Downloaded UVMapper classic.

Opened M4's .obj

Saved out the .uvs file

Opened a copy of V4 .obj in UVMapper

Imported the .uvs file

Changed the .cr2 of an instance of V4/Sasha-16 to search for the special .obj (two places to change it)

And voila!

This version of V4/Sasha-16 (I call him "Pasha") accepts M4 skin maps directly clicked in from the Poser library.

Thank you Kalypso for the specific instruction in this thread, and I also found it cited by Richard Haseltine at DAZ back in 2014.

::::: Opera :::::

P.S. I had no prior experience with UVMapper or altering .obj and .cr2 files prior to this project. Whew!