Well from my experience the name of the new supervisor file has to match the one in the ...\EMERGENCY 4\Data\Lang\en\Supervisor, i'm not certain if it works by simply pasting the new supervisor files in a mod's folder (i have tried once and it didn't work), to find all freeplay supervisor files just do a search in the supervisor folder for "SUPERV_EVENT", plus if you own the deluxe version of em4 the search will also show the deluxe freeplay supervisor files too.