making a COTS airframe survivable?

Hi you might remember me from such famous posts as “Combining the ARMY ARH and LUH”. I’m still writing that research paper by the way and I had a big issue come up.

If I wanted to take a COTS airframe (such as the EC-145 aka Lakota UH-72A) and take it into a tactical environment where it would be subject to enemy fire, then it would have to go thru Live Fire Testing. Platforms in the past which have been specifically manufactured for military purposes like Cobra, Blackhawk, and Apache were already built with this survivability issue in mind.

How do I “make” a COTS airframe more survivable? (A nail gun and kevlar?)
Whose responsibility is it? The vendor, tester, or customer?
Are there any COTS ARMY aircraft (rotary wing specifically) that were “beefed up” for ARMY use? If so, what is the process in altering an airframe?

I am getting confused as to when a platform goes thru a Live Fire Test and it is determined that a certain component is susceptible therefore some action must be taken to improve survivability & knowing that a platform will have to go thru live fire so you therefore modify the platform. Shoot first then modify? OR modify first then shoot?