As I worked to resolve errors with attempting to reference a User Parameter from within a Python Scripted User Parameter, I discovered the issue was previously mentioned 5 years ago in this thread:
When I double-clicked on a user parameter (‘DAYS_PRIOR’) in version 2023.2.1 (build 23774) within the Python Scripted Configuration interface, FME Form inserted: FME_MacroValuesa'DAYS_PRIOR']
In order to get the scripted parameter to function properly, I ended up changing the call to: fme.macroValuese'DAYS_PRIOR']
I also had to explicitly import the fme library.