Could be made working with some tweaks.
My idea would involve nppexec plugin and two versions
of NppExec.ini file because NppExec can be configured to run Compare
on notepad++ startup.
Basically, one NppExec.ini is configured with something like
and the other with default settings.
You create a batch file which gets executed when clicking the explorer context menu entry.
The batch file itself renames the default NppExec.ini to something like NppExec.ini.default
and the special one from, let’s say NppExec.ini_compare to NppExec.ini .
Then it starts npp exec with the parameter to open the two files and afterwards
renames the NppExec.inis back to default. Should work, I guess.
Don’t have windows - so can’t really test.