You can simply copy your subtitles to the video folders after cataloging is completed. In addition, if you want your subtitles to be included in a future subtitle definitions update (if they aren't already in) simply archive them all up, upload/post them online, and let me know the URL. I can ensure that they are recognized in the next definitions update so when you catalog your videos they automatically get included.
Note: The latest subtitle definitions are only available on Patreon, so if subtitles are important to you it is something I would recommend you consider. The latest subtitle definitions can detect and download over 15,000+ worth of English subtitles.