I actually did this in the Bulgarian league for my team.
First you edit your local team and under competitions make sure you put the league you want them to be. (i.e PRM).
Then if you just try to load the game PRM won't be playable, because it only allows 20 teams and there are 21.
Next you need to take out one team out of the PRM. For example if you want to replace Hull, you have to send them to the league your local team was (if the league was playable), otherwise if you just decide to send them to the Championship, you run into the same problem if the league not being playable, because there are too many teams. Then again you have to take one team from then and send them to another league and so on, until it is playable.
First you edit your local team and under competitions make sure you put the league you want them to be. (i.e PRM).
Then if you just try to load the game PRM won't be playable, because it only allows 20 teams and there are 21.
Next you need to take out one team out of the PRM. For example if you want to replace Hull, you have to send them to the league your local team was (if the league was playable), otherwise if you just decide to send them to the Championship, you run into the same problem if the league not being playable, because there are too many teams. Then again you have to take one team from then and send them to another league and so on, until it is playable.