Add CGI droids to Wrath of Kahn?
Add a terrible CGI jazz number to the opening of Final Frontier instead of Row Row Row Your Boat?
A scene where Kirk walks around one of the whales from Voyage Home and steps over their tail?
What would you add? Take a film and go to town.
The TNG sequel can be the 2 hour extended cut of the saucer disconnecting from the rest of the ship
Star Trek: Generations directors cut feature the saucer section crashing along the surface of Veridian III for 45 minutes