Since then, I gave into my overly curious nature and used some spare time to look into it.
Well, the situation is both more simple and more complicated.
For most of the text, it is in plain ASCII, so I was able to change the "years" in "Eighty years" to "Eighty zarnz" (just a random nonsense word) without trouble. FCEUX didn't give any trouble.
I was able to start a game and go into one of the rooms of the town, without any obvious problems, so when you say it crashes if you change something, I am a bit lost.
Does it crash after the text scrolls by? At which point exactly?
The complication for me is that I'm not sure where you're having trouble, in the first place.
However, with FCEUX you can easily set breakpoints and gradually narrow down problems, if you understand debugging and have the time and patience for it... if you upload a video to YouTube of the problem in action then I'd have some idea of what you mean by "crashing"... you said:
" it seems to screw up the entire game.[...] when I went to see the change the game crashed on a yellow-board screen with a text box at the bottom.)"
Well, so far, the game doesn't seem to crash when you carefully edit only the text.
Offhand, the initial letters might not be letters but pointers to sub-routines that set up the text display and push out the first character before returning. In other words, compound control codes. If that is the case, you shouldn't edit the initial letters but instead trace the problem and modify the routine.
To test for that, try what I said initially and try changing a non-initial letter.
Modifying and debugging takes a lot of time an patience, and you might need the help of a basic guide if you haven't done something like this before.... or a programmer minion/friend/cohort to extract and re-insert the text for you.