Addresses After Editing Events

I've been browsing the help files on this page and looking through the tools available and had a question about editing the hex events.  I have never edited a ROM before but my previous experience with hex and assembly left me with a question:

If I edit an existing event by adding actions that were not previously there, won't the additional data shift everything after it forward however many bytes it added, thus causing all of their address references to be off?  Can you move it to the end of the file and update the event trigger address to preserve the integrity of the surrounding data?  Do you just overwrite any data that comes after it instead of shifting it (the tutorial screenshots seemed to be overwriting)?