It never seemed to be possible at all. There wa one claim that a person’s friend could do it, but no evidence presented and no one has been able to recreate the result.
If you uninstall the app to refresh progress then yes, you will have to start completely over. Gems and any premium options you have made will not carry over.
It’s kind of a shame that it’s set up so that once you match with someone and start the conversation you’re stuck with them, but I get it too in case you change you’re mind about unmatching them and especially if you spent diamonds on them. Still, it would be nice to be able to unmatch with a character and start that story over if we wanted to pick someone else instead from that storyline group.