Maybe a better alternative would be giving some very regularly used weapons in each shipset an alternative fire mode, and when a weapon group with this is toggled it also switches targeting priority to what PD has. This could also be applied in reverse for PD weapons so that fitting them isn't as nearly as inefficient a choice as now. I think the alternate firing modes should also be inferior to the weapon it emulates to try to avoid making anything a bad choice as a weapon.
Some examples:
Light Autocannon - Switches ammunition from a kinetic energy penetrator to a canister filled with ball bearings (shrapnel damage). The sabot carrying the submunitions opens in the path of its target.
Tactical Laser - Reconfigure deformable mirror to allow for an increase in power, but at the expense of having a beam cross-sectional area so large range range is effectively halved.
Arbalest Autocannon - Equip calibration ammunition, far higher fire rate due to decrease in propellant heat with nylon projectile that does shrapnel damage on impact.
Mjolnir Cannon - Lower micro-capacitor electrical potential to allow for proximity sensor to scan beyond the plasma sheath. Will attempt to detonate when near a target. The reduction in charge and potential in the capacitor lowers damage considerably.