Of course the game will not longer work, by adding bytes of information you shift everything after those bytes, so when the code of the game looks for the exact part of a code or text, it is no longer there and reads the incorrect data.
If you want to change text, you have to either use the space already used by the text, or learn how the text routine work, locate free space on the rom and relocate the text there, changing the pointers that tell the game where it needs to look for each string of text.