Yeah, that is possible in Subtitle Edit. I use it all the time, exactly like you describe it.
You can save some time for OCR and editing the results if you just OCR the first and last 10 lines of a graphical subtitle.
Then use “Point Sync via another subtitle” to sync a downloaded subtitle to that. Works usually very well (unless you downloaded a subtitle which was for a different “cut” version).
There are some finer details when doing this.
If you try to sync a different language or different translation, the result are not always perfect. Sometime one subtitle combines several lines into one line. So you need to dig in a little bit more and find a few shorter lines, which are relatively isolated and so you can be certain that both subtitle are in sync around those lines.
