Do not attempt to use an NCE 5 amp / 10 amp / Power Pro / PH-Pro / CS02 system to program CVs>255 in program track mode using the Pro Cab. You will corrupt other CVs in the decoder.
Your options are:
1) Use the built in serial interface and a PC running JMRI / Decoder Pro. It knows how to work around the firmware bug in the Power Pro and it also takes care of setting the index CVs 31 & 32.
2) Use Program on Main but you MUST first manually set the correct values in both CVs 31 & 32 BEFORE changing any CV>255.
Depending in the type of NCE system you have AND the actual decoder, accessing and changing CVs above 255 might require a different method.
The 5amp PH-Pro has a firmware bug that prevents access to CVs above 255 on the program track ONLY.
You can use programming on the main with no issues.
The Power Cab has no such limitations.
Depending on the decoder might need to deal with indexing too:
To access CVs above 255 you might need to set one or two “indexing” CVs first.
Read this: https://dccwiki.com/Configuration_Variable#Indexed_CVs
Thanks to NCE "Super User" Dave Heap for this information.