Thanks for the kind words! I'm having a lot of fun with this stuff. It kind of feels like solving a puzzle, combined with like... digital archaeology maybe?
I totally feel you; I'm not nearly as skilled, and can't trace the compressed data back to a location in the ROM, but the little hacks I've done are really satisfying because it's identifying a thing you want to change, and solving the puzzle of how to make that happen!
If it starts to bug you another alternative would be to change "very hard" to something shorter. I considered "harder" but I didn't want to mess with the translation part too much, and honestly I think I like "very hard" more anyway. I also thought about something like "whoa!" since it looks like the original was "sugoi"?
The difficulty names are a little weird, and part of my decisions were based on the localisation of the original Star Stacker on Game Boy.
If you translate them literally, the Super Star Stacker difficulties are something like...
"It's a mess"
I considered going for "Easy, Normal, Hard" but the English GB version's difficulties are "Normal, Hard, Very Hard, Super Hard" with the hidden "Insane" difficulty. I felt like consistency between the two versions was important in that sense, and "Normal, Hard, Very Hard, Insane" has a good logical flow in terms of how it steps up.
I'm trying (and succeeding so far) to make the names use those graphics you made instead.
There's something remarkably cool about using them the way they were seemingly intended, when they weren't used that way in the official release for whatever reason.
Do be aware that I didn't see any text there for the hidden boss Gryll, and don't know if it lists her in that slot under any circumstances. If it does, I whipped up this matching text sprite. It's crammed into just two tiles, so hopefully it won't be difficult to fit. If you need to.