Hi Coolman nes, we're currently doing a Fifa 2020 (Fifa 95) for Mega Drive. This dat file, I think you can rename it to an extension, Graphic editors or Tile editors may open.
Or as Fast6191 said, open the game in that specific Tile editor.
Fast6191, as you'd said, romhackers don't care so much with Sports games? I agree with you, here on romhacking.net, because we don't have so much support from expert hackers on the topics.
But I think this can't be applied to South American guys and other people around the world, passionate by this type of games... lol... Here, we have tons of hacks for ISSS (Snes and Genesis), Fifa (All versions), Super Monaco GP and other sports games.