Unless you're a junker, you probably shouldnt be looting wrecks to begin with. There are very few fighter pilots or traders who have the necessary equipment to extract weapons and systems from a derelict ship successfully.
And if you are a junker, well... you can use damn near any weapon in the game.
This is one of those things which the game engine allows, but ideally should not happen.
It's plausible that different factions will have weapons which are not cross compatible.
So retro-fitting as such will be nearly impossible to not every layman's job.
As far as using enemies tanks (from the example before), yes that can be done, but what's being done here
is a bit different - more similar to extracting the main gun from a Panzer and putting it on a different tank...
I'm no one would do that...
<span style="font-family:Century Gothic">Spec - Independent Trader</span> Small Transport - Hauling without earning
Current Status: Inactive - Too Much Work and Travel