Methology Q reg. Time stretch

Hi all. Wondering how to go aboutt this without making a total mess.
The goal: several sibelius scores with a ton of tempo and time sig changes, to be sequenced in a single sonar project, slowed to 50percent, recorded over and sped back up.

Thoughts: open first midi, open all others and copy paste special them into the first in order including tempo and time changes.

Then what? How would one halve the speed without making a mess?

Then record, set audio to...groove clip is it?

Then speed back up how? It's super easy to just type half tempo for midi to respond to and audio set to stretch in the same way when there are no changes, but....