1) "Or do I simply modify one of those three files as needed, leave it in its current directory, and then use the UniController to select the chosen .ini file? " This is correct.
Although “Configuration File (php.ini) Path" shows C:\WINDOWS this path is ignored even if it contains a php.ini file. The configuration file loaded is that selected by UniController, on start-up PHP is forced to load only this file.
The php info “Loaded Configuration File” is the one that php is currently using.
2) “And I see the file name of the various earlier versions of PHP (e.g., ZeroXII_php_5_6_x.exe). But nowhere do I see a link to download the needed file(s). ”