For posterity's sake, I might as well do exactly as you directed though.
Spoiler:So I started with a clean 1.0 Fire Red Rom. I found 40 bytes of freespace at the offset 0x71A23C. I then paste-wrote (ctrl+b) the instructed bytes to this location.
Code:06 4A 12 78 88 79 90 42 02 D0 C8 79 90 42 03 D1 28 1C 70 BC 02 BC 08 47 01 48 00 47 B8 70 03 02 59 A8 0C 08
I then went to offset 0xCA840 and paste-wrote the below bytes:
The former four being ones you supplied, the latter four being the modified pointer to the new data I just added.Code:00 48 00 47 3D A2 71 08
I then opened XSE, opened my rom, pasted in the code in your first post that I immediately copied from said post and pressed compile. Below is the error I receive. The IMG tag will not work here for some unknown reason, so you will have to follow the link to the Imgur post I made manually.
https://imgur.com/a/SuxPdOs
Just a quick question as well: which version of XSE was used for this to work successfully? I was using version 1.0.1. I already tried to use the update function, but apparently support for this program has been discontinued and it could not check for a newer version.
Thanks for documenting your process so well! I just tried to recreate this by following the same steps on a clean ROM, and I wasn't able to reproduce the error. I checked the XSE version and mine is v1.1.1 - that is likely the issue. Maybe "bufferpartypokemon" is a keyword not recognized by older versions? You can try getting v1.1.1 from here and see if that solves the problem.