Recently I decided to demux a MKV file so I could edit some of the errors found in the subtitles, but when I try to remux the files, the subtitles completely lose their font style, color and layout. I know that the styles come from the TTF files that were demuxed from the MKV, but I just want to know how I can recombine these files so the subs can retain its original style.

Note: I've tried using the attachment method (with the specified "MIME type") on mkvmerge with no luck.