Thank for the helpful information Tim! I ran into exactly this problem and couldn't understand why the Required field didn't show up as a property in VST... I thought I was going mad. You do say "not available to .NET add-ins (natively)". What do you mean by "natively"? Can we get hold of the property programmatically by some other means?
I did find that the property is available in VBA and managed to set from within the Window_BeforeOpen handler. It worked as expected: the associated text label turned bold upon setting it. I tried this out of curiosity only. I have no interest in inter-mixing VST and VBA unless I really had to.
In this case, I got lucky. I thought I'd have to set the Required field dynamically, but it turns out I can live with it being static so setting it in Modifier was enough for me in this instance.
Do we know why the Required field is not available under VST, but is available in VBA? I'm sure this will come up again in my GP travels.
Paul