Indeed, but then I guess the string must be "Seed version" in our electrum, otherwise the whole verification system won't work.
So if I were to change that string, then the whole verification system would be pointless.
Yep, you also would have to use that same "Seed version" string for the verification as that is what they choose to use. I'm guessing they used that string as the key since the point of that is_new_seed function is to determine which version of the seed is being used.