You have a wrong understanding of how the rider logic works.
It is nothing more then a special case of a container. As a result, the rider is stored as a data list, so there is no physical object stored inside. That's just a visual trick they play on you..
However, a number of things can be changed using the riders logic :
- The visual appearance with the conditionstates : you can assign a different model to each of the riders. In your case you just need to make 3 different units that reflect the armament change.
-Each rider is assigned :
a modelcondition
a weaponset flag
an object status bit
a commandset override
a locomotor
As a result you can assign a different weapon to each rider. This , combined with a changed riders condition, will give the illusion you swap turrets/weapons.
As said, the only limitation on using this is that the basic properties (vision, health, turret properties, etc) of your unit stay the same, because in fact it stays the same unit. The model changes are only visually.