Yes, you’re totally right, i need to fix that, hardcoding it wasn’t a good idea.
Of course you can! 
Sure. Here:
FilmNegRGB_650_550_460-elle-V4-g10.icc (1.1 KB)
I created it by hacking the source code from the ninedegreesbelow tutorial, so i guess there shouldn’t be any licensing issue… (please correct me if i’m wrong)
Here it is compared to Rec2020:
… and to ProPhoto:
Which might explain the different result