Now I remember one of the problems with AI SEAD tactics. With the default load outs, they generally carry TALDS. They will usually swoop in, drop the TALDS, (DUCKS AWAY!!) circle back and re-engage. While there has been a lot of controversy on the effectiveness of TALD, the net result was that AI SEAD flights took a long time to get the job done, even if they finally did it, so it was ineffective to "REQUEST WEASELS" when pretty much over the target, or have a SEAD Flight alongside when you enter the target area and expect much assistance (or have a SEAD and TALD armed element in your flight given an "ATTACK AIR DEFENSES" Command as you reach the target area) Far better to have the SEAD flight precede the STRIKE by some time...(or give the element ATTACK AIR DEFENSES while the STRIKE ELEMENT circles back) as has been covered, but then you run the risk of SAM/AAA that were missed by the SEAD folks being awake and alert when the STRIKE flight came sauntering in.

There's no way to modify AI loadouts in the mission editor drop down menu?

I don't believe so. The custom loadouts for Player aircraft don't appear in the Dropdowns in the Mission Builder. But there must be a way to add them, as I think TSH added a few extras to the choices present in the original.