Safe to change OS and apply 3bar at same time?

I am in the process of building a base tune for my new project and have a quick question.

I am switching from my stock OS to a 12212156 OS in my silverado. I know I have to do a write entire for the change to take effect. I am also going to be applying a 3 bar OS.

Am I ok to apply the 3bar to the 12212156 OS and write entire to my truck all at the same time? or should I write entire the 12212156 OS THEN write entire again to apply the 3 bar OS?

Gen 3 or gen 4? I can move the thread there if you don't get any replies here.

Since a write entire always overwrites what the pcm currently has, you can make all the changes at once then write entire.
After that, write calibration only for all changes.

Thanks for the reply, it is a gen 3