All of us have been in this boat once or twice, where you format your PSVita back to stock and forget that you can’t activate it or you will have to update. If you are lucky and have a PS3 on hand you can reactivate it but for most people, they don’t, so they can’t use any of their backed up content. So you either have two options stay on lower FW with no content or just update so you can play your games again.
Well, Developer vita-activator and it does just like it says, it activates your PSVita.
Also, you will have to compile it and make the VPK so you can install it on HENkaku.
If you happen to give it a try, let us know if it worked for you in the comments below..
Update: Seems that I missed the vpk file or the GitHub got updated since this morning, but I probably just missed it.