Different Time signatures on different staves - HELP !

Hello !
I'm actually working on a midi mock-up of the "Superman March" by John Williams.
At measure 35, all the instruments are written with a key signature of 12/8, except the Violas and Cellos that are written in 4/4 !!!!
Later at measure 43, violons key signature turns to 4/4, while Cellos turning back to 12/8.
Finally, Violins and Violas return to a 12/8 key signature at measure 49.

I didn't find a way to do this in Musescore. Is it possible ? If not, any help is welcome..