Do you mean that you need the mask to be updated at runtime? Could you please expand a use-case a bit more? AFAIK, the mask cannot be refreshed during runtime. As stated in this blog post:
In addition to running when you click OK or Apply, mask initialization runs at the start of every simulation and update diagram, when you call set_param to modify the block, and when you are building the model as you drop the block into the system.
In general though, you can use the technique described in the documentation for Access Block Data During Simulation.
