Hello,How to make the Custom DB files of the game,so that I can make our own leagues from scratch???????

I would recommend taking an already existing mod file and using that to make changes to. I do want to caution you on a couple of things though - you cannot have more or less than 357 teams and you should keep the number of conferences the same. You will also need specific codes for conference schedules depending on if you are changing the number of teams in a conference. If you decide to go forward with building one let me know when its done and I can help you with those conference schedule codes

In the Demo,I was able to sim the season up to the post season tournaments, while having a different amount of teams and conferences. Made sure the schedules were correct for each conference. It gave me no errors. Is this just because it was a demo or will I run into issues in the full version?

I can confirm that during the awards and advancement to the next season, I got frozen up. No biggie. I'm actually buying and playing the games this year, thanks to some major advances and finally multiple team control. Thank you for adding this feature. Been hoping for a long time.