Can I ask a few more small questions?
I want to modify the words in the start menu
For example Bag = Pack
Where can I find the offset of the letters in the start menu?
Well, you can use this tool:
Hex Maniac Advance
With it you will be able to edit any text in the base. In addition to being able to edit any existing text in the base rom, you can also edit various other things in the rom.
But it's worth noting that as the rom was expanded (items, pokemon, moves, etc), some things the HMA won't be able to read correctly. So it's good to be aware of that.
All in all, HMA is a great tool. You can do a lot of things with it.