subtitle handling for optimised versions

Hi,
i started to have 2 optimised versions (720p and 480p) for all my movies.
in regards to the subtitles i understand that Plex is copying the subtitles for those versions next to the media file itself.

my question is now is Plex maintaining those subtitles in any way?
for example if i replace an english subtitle of the origin version, is it also replaced for all other versions of the movie?

Matt