I served in the 7th Psyop Group, the Reserve counterpart to the active-duty 4th POG. Although "reserve" is misleading: there was enough going on in the world to keep both units mostly active throughout the 90s. For example, my unit had all our Psyop Specialists on a regular rotation through Bosnia and Haiti during my period of service.
Anyway, there are some important regulations governing the use of U.S. Army Psyop forces. The top two are "always tell the truth" and "never target your own or allied forces".
Don't get me wrong. I wouldn't be surprised if the U.S. government lied and targeted its own and friendly people. It's just that the government wouldn't use the 4th or 7th POGs to do it, not without whistleblowing, court martials, and other major, serious problems.
The presence of Psyop units in Colombia indicate a fairly mundane, straightforward war-fighting strategy that makes use of propaganda tactics against enemy forces, in support of more conventional military tactics.
It may also, to a lesser degree, indicate Psyop elements acting in conjunction with Army Engineers and Civil Affairs units to carry out a "nation-building" mission. Psyop units are great for this kind of aid work, since they usually have a high number of linguists and cultural and communications experts (since that's basically what a Psyop Specialist is, really: a cultural communications expert).