All Things Event Hacking

You can use either 48 XX YY or 4B XX YY to have text appear during events. The difference is that when you use the 48 byte, you want the text to appear and dissappear very fast, without waiting for the player to press the a or b button to continue. When you use the byte 4B in front, it means you want the player to read the text and press a button before moving on. NPC's are given usually the 4B XX YY command so the game only continues after you press a button.

But yeah, some NPC dialogue is given through events, for example, strago's and relm's dialogue after you meet them:

CB/DCB3: 4B BB 07 Display dialogue STRAGO: What a beautiful day.
CB/DCB6: FE Return

CB/DCB7: 4B BC 07 Display dialogue RELM: Interceptor, please come back again and play!
CB/DCBA: FE Return

In any of these two, if you change the 07 byte to 87, the text box will be displayed at the bottom of the screen.

For in battle text and events, I'm not yet sure, I don't know how to manipulate in battle events yet.

Hope this helps :p