I might be late to the party on this but I haven't seen it mentioned any where so I thought I would throw it out there for any modders that hasn't figured it out yet.
You can now build a 35 Team PLAY NOW roster! This file is already set up with 3 extra team slots ready to be modded. Knight Hawks, Black Knights and Oilers are just NFL clones filled with Free Agents as place holders. I threw this together as a starting point for modders.
Please note until Frosty is done it is really touchy on what you change via Madden db editor because not all of the codes from M19 are the same in M20. So edit at your own risk prior to the release of frosty.
Also the 3 extra teams are currently only available for Play Now mode. The franchise roster spot shows it has 35 available team slots also but the file is empty or I just haven't stubmled on to the correct file yet.
*Note*
To add 3 extra spots to your already made roster you have to delete the free agent list in from the TEAM table via Madden db editor. It does not remove the Free agents from the game, it just opens up another team spot. When you go in to the free agents list it loads up as it's supposed to.
Enjoy and MAKE BACK UPS before editing.
DOWNLOAD LINK
https://trello.com/c/otorm87G
*Last side note*
This makes me wonder if it's possible some where in Frosty to change the capacity number of allowed teams in a table. My guess it no but something to keep an eye out for while digging through Frosty.