Thanks folks for ideas, but I was talking about just basically ‘hiding’ the conversations by pushing them to the ‘archive’ folder. (I already backup with SMS Backup/Restore).
I decided to write a quick/dirty (no guarantees) tampermonkey script to do exactly what I wanted. If anyone else needs something similar, they can take a look here: gist.github.com/…/47c900978866770cdff934f6cd78366…