For the Civilian ones (people & vehicles), you can use location logics if you want them to only populate those places. If you place the logics by themselves without synching to anything, they will populate the entire map.
It's in the missions pbo. Missions/som/data/scripts/secops
Quick note: I've added the ability to alter the minimum and maximum distance SecOps are generated at and the frequency of starting random SecOps. Look for this in an upcoming (after 1.01) patch.
What is already possible: without modifying the core SOM scripts (not recommended), you can create new SecOps in some add-on and define them in CfgSecOps. The SOM will automatically be able to use them. Eventually there could be a long list of community SecOps if anybody likes making them Worry not, documentation is coming.
Thanks for the update.
More informations at Biki: http://community.bistudio.com/wiki/Ambient_Civilians