help with v4.1

the original version of musescore allowed for you to have different key signatures for different staves -- how can I make this happen in 4.1? it seems whenever I add a key sig it changes it for the whole system

this one is probably a stretch -- but is it possible to do this with time signatures as well? i'd like to have a 4/4 with one instrument playing in 12/8. if not I can just use triplets