The {plex} format automatically removes (1) (2) (1/2) part numbers from the end of the episode title. If you want to keep the (1) (2) part numbers then you can either inject them into {plex} or just use {t} in your own custom format.
e.g. Stargate SG-1 - S01E01 - Children of the Gods (1)
How do I apply the replacePart filter so the episode filename looks like this
TV.Show.Title.S00E00.Episode.Title.Part.1.WEBRip.x264-GROUP.mkv
The t.replacepart('Part.$1') doesn't work and repeats the filenames twice