Apparently, Tecmo Bowl is one of the most modded games ever. Much of this information is found on the tecmobowl.org forums, along with more software.
- Tecmo Bowl Team Manager
Tecmo Bowl is the simplest title. Tecmo Super Bowl got a little more complex, so the editor is more complex. Personally, as I was tinkering, I enjoyed replaying the original vs Tecmo Super Bowl, but that's just me. All things aside, you need an editor.
- Tecmo Bowl Manager: Windows download
- Tecmo Super Bowl Manager: Windows download, Mac download
These programs allow you to load the game file (ROM, see below) and edit team names and rosters through a desktop app. If you're on a Mac and want to run Tecmo Bowl Manager, I can send more detailed instructions, because I got that running as well.