Put every crew saving hullmod on the ship you want to select d-mods for. Remove all weapons from the ship. Find a pirate corsair. Save. Fight the corsair only deploying the ship to be destroyed, and a ship you pilot that can kill said ship. Kill it, kill the pirates, recover and check the d-mods. If you got one that you wanted, save and repeat. If you didn't, reload.
It shouldn't take more than an hour using this method for an entire fleet. This is also the method used for getting ideal officers. You just max out their XP, save, and then level up.
It's not quite that simple. If you are trying to pick the "best" (i.e. affects the ship the least) 5 dmods out of 12, assuming you get 1 dmod per fight, on the first one you have a 5/12 chance of getting one that's okay. But when going for the 4th one, you have a 2 in 9 chance, and for the 5th on, you have a 1 in 8 chance. So to get the perfect 5 dmods, it's basically (5/12) * (4/11) * (3/10) * (2/9) * (1/8) = 120/95040 or 1/792. So on average you'd have to fight 792 times to get the right combination of 5 dmods. And do that for every ship in your fleet.
I find that it's relatively easy to get 1 or 2 dmods that you want, but beyond that, it's basically not practical. And just getting the 2nd one for your whole fleet takes a bit of effort. Anything beyond that will basically exist only because of the Console Commands mod or direct savefile editing.
Incidentally, where I found DO to have the greatest benefit is around 2-3 dmods. You can usually find 1-2 dmods that don't affect the ship that much. But beyond that, most of the dmods will really hurt the ship somehow, and then it becomes not that useful.
Is the main benefit of SD the ability to spam LP Brawlers without wasting officers on them? They punch well above their DP cost, and Combat Endurance shores up their main weakness.
SD is useful in the early game in general, when you don't have officers built up. It's just that LP Brawlers work pretty well even without officers, so SD makes them work even better.
@Vanshilar - where do you find LP Brawlers in the early game? I almost never see them for sale in Chalcedon and Epiphany. When I defeat LP fleets, recovering the Brawlers (if they are even available) almost always cost story points.
Only place I've found to buy 2-3 LP Brawlers at once are LP bases in deep space.
There is usually at least 1-3 patrol fleets with LP Brawlers near their planets, plus I check the planets each month. The markets refresh their wares after 30 days. So I basically go in to check the market first, then I search nearby for the patrol fleets (since after I kill their patrol fleets, the market may not let me back in for a while). Yes if there are any hidden bases nearby I'll look at those too.