Originally Posted by White Rabbit

You can't, not without first owning 1.23 JJ2, because 1.23 JCS comes with 1.23 JJ2, which is different from TSF JJ2, and TSF JJ2 only has TSF JCS, and that won't work with 1.23 JJ2, so if you want your tileset to be compatible for both versions, only use 1.23 JCS.