But if the change in the name is the problem, maybe the pic-as.exe can be renamed and the MCS can find it and use it
Unfortunately there's more to it than just a name change.

Assembly code written for MPASM will not work with pic-as (which is part of the XC8 V2.20 package), and has to be re-written to be compatible.
The upshot to this is any new chips added after MPLABX 5.35 (mpasmx 5.87) will not work with PBP.

if the compiler does not support the new PIC's there is no point in updating to new MPLABX assembler, right?
Correct

Some documents about pic-as:
MPASM to MPLAB XC8 PIC Assembler Migration Guide https://www.microchip.com/mymicrochi...name=en1001804
MPLAB XC8 PIC Assembler Users Guide https://www.microchip.com/mymicrochi...name=en1001821
MPLAB XC8 PIC Assembler Users Guide for Embedded Engineers https://www.microchip.com/mymicrochi...name=en1002091