You could try pointer hacking.
[pretty straightforward name; you're editing a part of the file header where the game "points" to "start" text and "end" text]
Worst case scenario you could see if there's extra space at the end of the file, write in any overflowing text and modify the pointers to "point" there...though pointers only point to one place at a time.
The downside is that you'll still have the "text box" limit...think of this as how many times the character says something in field dialogue before another character starts speaking. If character A has two "boxes" of dialogue and then character B says something, character A has a box limit of only those two boxes. You could change the speaking characters maybe if the dialogue container file is simplistic enough...but that'd go against what you want.
Basically, pointer hacking is good if it's just adding like 5 extra characters in a line...and if you put in too much text, the text box will overflow and it'll look goofy with the text going off to the side.
It sounds scary advanced but it's...pretty easy once you get the hang of it...though, it depends from game to game. Some games might have goofy methods of displaying text/pointers, or the way pointers are edited/text is modified may differ from game to game and publisher to publisher.
If one of you on the team is extra daring and knows what they're doing you could also write a dialogue editor....but that's not really something to be taken lightly ._.
There might be other people on the forum more experienced with this stuff [Noitora, psycoblaster if they still post] and have better, more efficient methods of texthacking, but pointerhacking's the best way I know to get around the text limit without modifying the font or the kerning of the text (which is what some of the ~extreme, superior text hackers~ here do)
but yeah!!!!!
