I used a sheet of Uschi plank decal. because it was going on a broad surface in a structure (about 8' x 12' in 1:35 scale) I didn't trust my ability to "water-slide" it. I left it on the backing paper and used 3M transfer tape, full coverage, to hold it down. no bubbles or folds. this is a very handy material to have in the drawer and comes into use on a number of things. I believe Paul Budzik was responsible for making it known to me in one of his excellent videos. http://paulbudzik.com/tools-techniques/index.html

the Uschi instructions suggest toning down the finished decal with acrylic paints & varnish.
https://www.uschivdr.com/downloads/

my question: will an airbrushing over the decal make it act like a decal and cause separation?

I would try to use several light coat not only to seal, but tone down the graphics a bit, too.

thanks for any direction!

I did it in a more conventional way for the Uschi wood grain decals on my Gotha.
After application , some light coats of 50/50 IPA and Future sprayed at around 15-20 lbs.
Gives a tough, thin ,hard coating.