split and join measures

My ignorance mislead me again. I was using wrong terminology.
What I referred to as split measures is called in Musescore system break.
And indeed clicking enter on the bar before the last measure in a system will move it to the next system.
What I'm looking for is the opposite action.
I want to move the first measure in a system to the last measure in the previous system without unifying measures but as separate measures.
Of course I can always add an empty measure at the end of a system and copy the first measure in the next system to the empty measure. But there must be a more simple way like system break.
ctrl+del unifies the first measure in a system with the last measure in the previous system, thus spoiling the time signature.
So how do I move the first measure in a system to the last measure in the previous system as a separate independent measure?
thank you