Yes, the only technique for lowering Wisdom (at least currently) is to interrogate someone and beat it out of them using violence. Instead of playing Music to raise the Heart of the Agents and turn them Liberal (which doesn't reduce their Wisdom at all), you could ask them out on dates, then kidnap and interrogate them, and beat the Wisdom out of them. Of course I have usually found that people I successfully interrogate usually end up with quite low Heart, much lower than if I converted them to the Liberal Cause by playing a Guitar at them. Plus they still have some Wisdom, too, usually.
Anyway, what you are currently doing, turning them Liberal by playing your Guitar, is a very good technique and results in them having higher stats than if you interrogated them. This allows their skills (specifically Art and Music) to reach higher levels. Yes, they may have higher Wisdom than if you interrogated them, but they have higher Heart too, and so that particular trade-off is worth it. Just avoid having them do anything to increase their Wisdom even higher and you should be fine. Their Wisdom probably won't be a problem if they're a combat squad, unless you encounter Conservatives that use special argument-based attacks, such as Radio Personalities, Cable News Anchors, Hangin' Judges, Police Negotiators, etc. But if you have good enough weapons (read: guns) and high enough weapons skills, you should be able to kill anyone who uses a special argument-based attack before they can give you even more Wisdom. My weapon of choice for combat squads is, of course, the AA-12 Auto Shotgun. And the armor for them? Heavy Body Armor, of course.