First of all, thanks a ton for releasing this
The situation surrounding this game's release is extremely confusing tbh, even moreso than with SNES Picross.
So, you basically have:1/ Sutte Hakkun Event version (Satellaview)
- 11/1997 - 50+5 levels
ROM: Sutte Hakkun - Event Version (Japan) (BS)2/ Sutte Hakkun (NP)
- 8/1998 - expansion to #1, 110 levels
ROM: Sutte Hakkun (Japan)3/ Sutte Hakkun BS Version 2 (Satellaview)
- 10/1998 - remake of #1 w/ new content, 30+3 levels
ROM: Sutte Hakkun - BS Version 2 (Japan) (xxxx-06-03) (BS), Sutte Hakkun - BS Version 2 (Japan) (xxxx-10-08) (BS)4/ Sutte Hakkun '98 Winter Event version (Satellaview)
- 12/1998 - another remake of #1 w/ new content, 30+3 levels
ROM: Sutte Hakkun - 98 Fuyu Event Version (Japan) (BS)5/ Sutte Hakkun (ROM)
- 6/1999 - identical to #2 (NP), different packaging
ROM: Sutte Hakkun (Japan)
Also on the Japanese Virtual Console.
The version currently translated.
That means some of the new content in versions 3 and 4 might have never carried over to this cartridge release, and it's not clear whether the cartridge version kept everything from the initial release.
About the modding potential, honestly if I were in your shoes I would look into whether a similar file structure exists in the alternate versions, whether they have any exclusive levels, and port them to the cartridge release, since honestly replaying the forced tutorials and first few levels for every version isn't something most would love to bother with.