Ok, this came to me quite suddenly, so it may be a bunch of arse.
Basically, another set of weapon mods.
These would directly affect the weapon stats that a weapon would have.
The two most obvious ones are:
+5% over all dmg per burst (not the 178% stat)
-5% over all freq.
-5% over all dmg per burst (not the 178% stat)
+5% over all freq.
And variations thereof.
No change to the overall dmg output, but you would be able to modify your weapon to your playstyle.
Would not change the skilling to reach the caps (the end result dmg/freqs simply being modified).
For example:
A player caps a weapon X, which he gets 500 dmg and 100 rpm on.
He installs the first mod, getting 525 dmg and 95 rpm on.
The actual skilling required to cap does not change.