I tried to use the weighting command in the mission scripts:
- type: milit
missionWeights:
0:
STR_ALIEN_HARVEST: 1
STR_ALIEN_RESEARCH: 100
useTable: false
startDelay: 150
targetBaseOdds: 100
However, the above code spawns approximately 50% of HARVEST and RESEARCH missions.
I think one can circumvent this with "executionOdds", but I just wanted to notify others.