The AI is stupid, and cannot be modded.
You can use an ability to destroy the SP and spawn a constructor ship.
Then you must find an Autocast Condition for when to use this ability, as afaik the AI only uses autocast to use abilities. Try "OnlyWithNoOrder" from the Scout's Explore ability, or search for other similar conditions.
Other possibilities would include making the constructor ship itself the siege platform with an autocasted sieging ability, making the platform revert automatically after a set time, or maybe you can use the OnBuffFinish trigger to revert all SPs when the planet dies (A buff that affects all platforms in orbit, finishes OnOwnerChanged and kills the SP, spawning a constructor OnBuffFinish, use ApplyBuffToSelf followed by LastSpawnerNoLongerHasBuff to make sure you only affect SPs, which you give a dummy buff that LastSpawner... can check for)
Don't make the SPs Starbases though, as there's a limit on the # of SBs allowed on a planet, regardless of type (unless you want to prevent the player from also deploying an Orkulus of course)