Finally, digging a lot in the Behaviors menu, I managed to find how to control the HPC sim levers using the Lvars "POSITION_HPC_1" and "POSITION_HPC_2" (HPC levers left and right), using the WASM function "execute_calculator_code()": "n (>L:POSITION_HPC_1)" or "n (>L:POSITION_HPC_2)", where n = 0 (FEATHER), 34 (OFF), 63 (ON), or 100 (HSWL).
Mapping 2 levers of my home cockpit to this code, I could for instance switch OFF an engine and then feather the prop.