The best I have been able to do is delay the commencement of AI raider spawns until half-way through the scenario where the player will have better gear using the "condition" of the module. Still interested if there's a way to alter frequency of AI raider spawns, though.

Not really at the moment - it's one of the reasons I want to upgrade the AI module soon.

That flexibility would be very useful. Thanks.

Perhaps consider an option like Chance of spawn (user input value) per time-interval-a (user input value) - with a guaranteed spawn per time-interval-b (user input-value). All capped by population factor.
Default something like:
100% per minute (which will be capped by Population factor).

Then those who want it less busy could set something like:
30% per 8 minutes and guaranteed once per 48 minutes.

For anyone watching, what I did is control the module with a public variable.
The public variable I put in the condition part of the AI module, in parentheses. I found it does not work without the parentheses.
When it is time to turn on AI raider spawning I set the public variable to true, declare it, then sleep for how long I want the AI raiders to spawn. Then I set it back to false; turning off the AI raider spawn.

You may not have to make it public with the publicVariable declaration after changing the value. I do it anyway as prep for making MP scenarios and the process-cost is as low as possible in this context (just setting a boolean) .