Is it "safe" to use KM to manipulate the Keyboard Maestro Macros.plist document? Specifically, since cron triggers can't be input as variables, I could use a macro to prompt for %Variable%CronString% and %Variable%UID%, then search the Keyboard Maestro Macros.plist for:
Cron</key>\n\t+([ \d* ]*)</string>\n\t+MacroTriggerType</key>\n\t+Cron</string>\n\t+</dict>\n\t+</array>\n\t+UID</key>\n\t+%Variable%UID%</string>
to be sure I'm manipulating the right macro, then replace \1 (the capture group that includes the current cron trigger) with %Variable%CronString%.
I'm just a bit scared to actually try it.