Sir you had my curiosity, now yo have my ATTENTION
The only difference between the Knight Hammer and the standard Executor is the models it points to. If you go into the space units for the IR, and change the Generic_Executor (I think that's what it's called, I'm not on a machien that has it installed) model to that of the stealth Executor, all Executors you'd build would be the stealth executor. Also, Kaine would be in a stealth executor because he uses the "variant" flag to the standard Executor.
You could also, if you wished to play as the PA with Kaine in a stealth, change Kaines "variant of" string to the Knight Hammer (again, I believe that's how they have it coded in the xml's) from Generic Executor, and it would have him being in a stealth Executor
At one point I was bored and I added the Sovereign to the PA, had Kaine in a stealth Executor, added the Vengeance (with the build button of the Executor though) Dreadnought as a buildable unit, etc. All these things are SUPER simple, as they're simply xml changes.
On one of my machines I even changed the "variant of" flags on the PA units so that they keep their fighter complement through all 5 eras, regardless of what the IR fighter units are. So the VSD-II's never get Tie/D automated fighters in era 3, etc.