The alien character played by Mandy Patinkin was originally going to be named George Jetson but Hanna-Barbera wouldn't give the rights to the name. The decision to call his character 'George' in the movie was kept as an in-joke.
Prior to theatrical release, Alien Nation was heavily re-edited in post production in order to be shorter. Originally it was supposed to be released in summer but due to the drastic re-editing it was released in October. Post production re-editing is also one of the reasons why Jerry Goldsmith's original score had to be removed and replaced.
Jerry Goldsmith's synthetic and score was rejected early in post production for being "too weird" and replaced with music by Curt Sobel. Jerry Goldsmith's rejected score was released in Spring 2005 as a Varese Sarabande CD Club Release limited to 3000 copies.
Theatrical trailer shows parts of deleted fight scene between Sykes and Kipling that happens right after Harcourt overdoses and seemingly dies. In the movie Kipling is last seen groaning and regaining consciousness before his car explodes. In deleted fight scene Kipling knocks Sykes on ground and is about to kill him when George/San Francisco shoots Kipling with Sykes's handgun and kills him.
Originally in the scene where Sykes is talking with Cassandra in night club, there was a part where George is searching through the rooms (this is why Sykes is pointing him to go out in the earlier scene) when suddenly he is attacked by another newcomer called Todd Watson. When Watson tries to escape Sykes and George chase after him and manage to get him. After questioning him, they let him go but when they leave Watson is knocked out by Harcourt's men and taken to the beach. In the scene where Harcourt talks with newcomer who he calls Strader, he is actually talking with Watson but this scene was obviously changed during re-editing, which is why Harcourt is not shown saying "Mr. Strader" onscreen. Later in the movie when Strader's dead body is found on the beach he has two bullet holes in his chest, but as seen in earlier scene newcomer "Strader", who is actually Watson, is killed by sea water and he also wears different clothes. Later scene where Cassandra tries to kill Harcourt when she realizes that he killed Strader was also changed, originally in the scene Harcourt admitted killing Watson, her boyfriend, which is why she tries to kill him. Also in the scene where Sykes and George are chasing after Harcourt and Kipling there is a part where Sykes knocks out one newcomer that came out of nowhere. If you look at the clothes that this newcomer wears you can see that it's same newcomer who was beaten and killed by Harcourt's men on the beach, Todd Watson. This scene was originally part of the previously mentioned chase scene in the middle of the movie where Sykes and George are going after him. This also explains continuity mistake where Sykes is first seen going down the stairs with his gun, then when he fights with newcomer he doesn't have his gun, then when scene cuts to George pointing his gun at police car that Harcourt and Kipling took Sykes is again seen in background running down the stairs carrying his gun.