Nuh-uh. Even the most simplest level which is 1.23 compatiable, if made in TSF JCS, will not work in 1.23.
Example: If you're making a level in 1.23 JCS, it will obviously work in 1.23. But say you accidently open it in the TSF JCS and save it. Boom. No more working with 1.23. (I'm pretty sure.)
|