Hello Oleg,
I think that this can be achieved through a
custom action.
For instance, you said that you are saving the user's input into a property. That property can be retrieved in your custom action, stored in a variable and then you can apply the regular expression on that variable. For more information about this, please have a look on our
"How to set an installer property using custom actions" article which I think you may find useful.
Since the custom action will be triggered from a dialog control, you should add it (in the "Custom Actions" page) as a custom action
without sequence. In order to add a custom action without sequence, all you have to do is to press the
"Add custom action without sequence" button which is placed to the right side of the custom action's name.
Hope this helps.
All the best,
Catalin