Hi @Canapin
I know your pain. After our original migration, we wrote a lot of custom Ruby code to clean up over a decade of code copy-and-pasted from every corner of the planet; not to mention all the mojibake and strange char sets; and not to mention all the various bbcodes which were nested which needed a lot of Ruby-ism to clean up nicely during migration.
It was non-trivial to do and took a long time (and countless migration attempts); but were / are primarily a coding forum, so if your forum is mostly only text (and not code), it should be more straight-forward.
Our team had to write a lot of “somewhat complex escape this and that” REGEX as well; because converting all that legacy nested bbcode to markdown is not trivial when people posted so much nested bbcode over the years. We also stripped out a lot of bbcode which we thought added little value years after posted.
To answer your original question above:
Yes, you can just comment out the methods you want to skip in the migration script.
We actually completely rewrote much of the migration methods, but they were a very good starting point and so very useful, considering vB3 migration was and remains unsupported.