Identifying free space

I've been working periodically on my own edit of FF6 for several years now; the file itself has been extensively patched and edited in various ways, mostly via FF3usME and IPS though I've done a little bit of hex editing here and there despite my essentially negligible understanding thereof.  Right now, I'm trying to implement a change to the Row mechanic; I had a patch created with information I sourced here awhile ago, it works on a fresh FF3 ROM but the game crashes after a fight when I implement it onto my version. I assume this happens because the patch is replacing some essential piece of code in the game's data, though as yet I am unable to find a suitable empty space for the code.

The ROM is headerless and expanded for the purposes of lengthening the names of enemy special attacks in FF3usME, and perhaps in other ways. I want to know if there is a reliable means of identifying free space in the ROM as to avoid replacing essential code.  Any assistance in this regard will be greatly appreciated; forgive me if this information is provided elsewhere on the site, I was unable to locate an answer thus far.

Thank you!

From the Wiki: https://www.ff6hacking.com/wiki/doku.php...used_space

Oh, yes, we are presently using this document while trying to implement the patch! To clarify, I wanted to know if there was a means of analyzing the ROM file to determine which addresses are not in use by the game or any patches which have been applied to it.

Ah I see. Well, I may not be answering this correctly again, but in terms of knowing which patches take up what space and might conflict, there's a patch conflict finder: https://www.romhacking.net/utilities/1386/

Free space in FF6 is filled with bytes reading "FF". I tend to open a hex editor and search for a string of 32 FFs. That generally helps me find free space.