First you need to make sure whether the parameter that you wish to change during simulation is running is a tunable parameter or not. For example, the parameter in Gain block is a tunable parameter. Also, you need to modify the setting at the "Simulation" -> "Simulation parameters..." -> "Advance" -> Check "Inline parameters" -> "Configure...".
If you can share which built-in motor and which motor that you wish to tune during simulation is running, probably we can find other approach to implement it.