Yes, this is easily doable. A pretty simple if statement to check if a player with that license has a character created (a mysql query would probably work best), if they do, trigger your spawn event. If they don't, load the multicharacter so they can create their character. All be doable within your multicharacter script.
Things worth noting, if you use this system, players will need to contact you directly to have a character deleted. Which could cause you hassle, and there's really not much way around this if you want to completely remove character selection for players with characters already.
A fix for this could be an option at your city hall to delete the character, you could use a prompt or target that just triggers the character deletion event that already exists in most cores, and is probably in whatever multicharacter you have. But it is risky, and you should definitely include a confirmation for the player just to make sure they don't do it accidentally.
