Finally; the quest for my own holy grail is complete: The ICEBOX.ROM.
Ever since I got the NoV-32 and now lately NoV-64, I have wanted a way to automatically switch the RAM blocks via a FOCAL program. Having searched for a ROM that makes this possible, the conclusion was that no such ROM exists. So, I looked at many of the really good ROMs out there to find one that I could modify. The choice became Angell Martin's TOOLBOX.ROM. With help from Peter Platzer, I got the SRC file, got up to speed on the SDK41 (thanks Warren Furlow) and added RROM (read the value of any address) and WROM (write a value to HEPAX or other MLDL RAM). The last one makes it possible to write the appropriate value to the address 4100 that governs which RAM block is active.
You will find the ICEBOX.ROM and its source file at the UC-41 website as well as a FOCAL program that shows how to use the functions to automate the block switching.
Hope this is of use to anyone.
A big thanks to Diego Diaz for keeping the HP-41 my primary tech interest :-)