I have two schools of thought on this. One one hand, I feel that Saban would like to do as little re-shooting as possible if/when Gokaiger is adapted.
However, in order to do that, it would require at least some explanation as to some of the ranger outfits we've never seen before. Could easily be a type of deal they do with the beginning of every Samurai episode, giving a brief history before the show starts. Face it, in a show that has time travel, space travel, multiple dimensions, and the like, it should be relatively easy to find an out to explain the Goranger costumes.
Or he could go the re-shoot any scene that has a non MMPR-WF costume. I use MMPR-WF because of the recent discussion on whether or not Disney era seasons are in continuity. Also considering the multi-verse nature of sci-fi, it shouldn't be too difficult to have a scene with NS-JF (or even RPM if they want to count that one) in it as being a different timeline, dimension, etc. And since the Disney seasons were seen in the U.S., kids who have seen them in some fashion will be familiar with those outfits.