Updating custom workflow activites with additional input parameters

While developing new or extending existing custom workflow activies you might experience a problem that new or updated  input parameters will not show up on the workflow designer UI.

In the Plugin Registrations tool you successfully updated the assembly, but still it does not show up on the UI.

A simple trick solves the issue:

In the Plugin Registration Tool select the workflow activity that you want to update and press the save button in the properties section.