Evo šta piše u helpu:
1.7 Custom formats
This feature makes possible to save a subtitle file in a format that Subtitle Workshop doesn't support,
or to easily create your own format or text files with subtitles. This option is only to save files,
if you do this in a format that Subtitle Workshop doesn't support, reading the file will not be possible.
Dakle - nema pomoći u subtitle workshopu što se tiče učitavanja fajlova koji su snimljeni u nekom custom formatu.
Uz neki tekst editor i malo search&replace moguće je titlove snimljene u custom formatu pretvoriti u normalan (npr) subrip ili microdvd format.