Fixing pause durations, incorrect time signature

HI everyone,

amazing support here, I always learn a lot. Thanks for that!

I am sharing a sheet and a PDF import, which need some fixes, and I would like to hear from your experience about what is the best approach to fix.

• Key signature is Bb/Gm; what is the best way to change it and keep all natural E's in place, without messing the E♮'s
  {\displaystyle \natural }?
• How to remove the 3/4 bar without changing the notes values after it?
• How to change a pause duration without changing the other notes/pauses within a beat?

Any hints on how
Amazing work of the PDF import btw, just some tweaking to make it 100%.