If a Simscape™ parameter is potentially run-time configurable, a configuration setting appears on the tab that contains the settings for the parameter. If the setting is enabled, you can use it to specify the parameter as either a run-time or compile-time configurable parameter. If the configuration setting is not visible, then either the parameter is strictly compile-time configurable or the Simscape option for showing run-time parameter settings is not enabled. To see how to enable the option, see Show Simscape Run-Time Parameter Settings.
If you use an expression to define a variable for a Simscape run-time parameter, you might not be able to change the parameter without model recompilation. When an unsupported expression is encountered during code generation, a warning is issued and the equivalent numeric value is generated in the code. For information on the limitations for using expressions for run-time configurable parameters, see Tunable Expression Limitations (Simulink Coder).
If you change the value of a Simscape run-time parameter during a simulation, the results do not reflect the value change. For a run-time configurable parameter change to take effect, you make the change when the simulation is stopped. To see how to change the value of a Simscape run-time parameter, see Specify and Change a Simscape Run-Time Parameter and Change Parameter Values on Target Hardware.