While your simulation is running, double click the block to open its parameter dialog. If the parameter is greyed out, it can not be changed during simulation. I tried and it seems that the parameters for the Delay Line block can not be changed during simulation. Other block, e.g. the Gain block, its gain parameter can be changed while the simulation is running.
This info is available at document: Simulink>Working with blocks>Working with block parameters>Changing the value of block parameters during simulation
