Making an applications stay on the phone "permanently" I would like to be able to make an Android application remain on the phone even after a factory reset and/or a system upgrade.

Some people suggested that the way to accomplish this is to root the phone put the desired application in the system/app and unroot the phone.

What I was wondering is - is there a less aggressive way (avoiding rooting the phone) to accomplish this? What would be the standard way to accomplish this?
I would say no. 

If you want to completely copy app from phone to another storage you need usually root. And for making app as a system app, you need unfortunately root as well.