Hi Taylor,
This is possible using our existing, but not yet documented plugin architecture for ST-Sim and SyncroSim. There are currently two new prototype examples of people doing this. TNC Nevada is using a dynamic link to a sage grouse habitat suitability model written in R which is used to modify ecological restoration probabilities in space each timestep. USGS is linking ST-Sim to the FARSITE fire growth model to define where fires happen on the landscape for each timestep. Both these examples allow for feedback between the state of the landscape at a particular timestep and the dynamics of the external model which in return affects transition probabilities in space. The main interface for this is the use of transition spatial multipliers. Because the functionality is brand new, we are still in the process of developing the documentation and some simple examples on how to link external models. This should all be ready quite soon.
Regards,
Leonardo