I’m curious… Couldn’t you just export it with the color grade, import that file back in and then add on the grain?
I decided to try this out. I exported the file in GoPro Cineform, put that file in a new project for the grain, copied and pasted the overlays, and exported yet another GoPro Cineform file. I then deleted the original file to save my disk space, and converted the grain file to mp4 via Handbrake. All in all, the first file was about 87gb, the grain file, 127gb, and the converted Handbrake file 10gb. It’s not my favorite way to export a file, but it did work. The downside is that the final result is very bare bones. Only one audio track, no chapter markers, no commentary, etc. It’s just the edit itself in 5.1 surround, and nothing else. So, those issues need to be taken care of before I can be satisfied with this. But it did work, so this option is worth keeping on the table.