The novel for TFF came out before the film. I was quite excited about the film when I read it because it is MUCH better than the final filmed product. Many little plot holes are filled in and some of the goofy awkwardness of the humor is gone. One of these fan productions should re-make this film based on the book.
Don't get too confused here. There is the novel "Final Frontier" by Diane Carey (January 1988), which is the story of Captain Robert April, Dr Sarah Poole-April and Jim Kirk's father, George Samuel Kirk Sr - and then there's "ST V: The Final Frontier" by JM Dillard (June 1989).
All of the ST movie novelizations came out a matter of days before the films upon which they were based. Sure, JM Dillard filled in a few plot holes that the film didn't, but there was no significant differences that would require a fan film to
remake the whole movie - you just need to splice in
Galaxy Quest's orange rock creature and you're set!