No, that isn't how it works. The routine is the same, but the offsets are different. I also don't have the offsets that you want because although the methodology I used is similar, I changed different parts of the battle engine. I was initially going to post the stance change routine for FireRed, but it is unfortunately too intermingled with a number of other abilities, attacks, and items. It also uses a number of functions that I wrote in C, making it unfeasible to post in the ability resource thread as a standalone. Therefore, in order to give you the offsets that you want, I'd basically be restarting it for you from scratch.
In order to port it, you'll have to use the FireRed equivalent of offsets, for which you'll need to have an understanding of both battlescripts and asm. I recommend you dig through the ability resource threads/move resource threads and do some asm studying. If you don't understand what you're inserting in your ROM, then the Emerald attacks and abilities are useless to you. If you do a bit of studying first, you'll understand that even the Emerald exclusive posts contain 99% of what you need.