SampleCustomizer on Table

It should be possible without a customizer:

In the template for CCC_isResident do something like 

Base.Columns("CCC_FirstName_en").MinLen = CInt(IIf($CCC_isResident$, 1, 0))

Important is the self-reference. It does work for my custom table, but I don't see a reason why it should not work for Person.

Also you might need to initialize the value in the OnLoaded Script. 

I vaguely remember that I had to force a re-rendering in the WebPortal, but not sure if that was connected to this.

When I remember it correctly, does this solution not work if you are using an application server connection. In regards to the web portal, the object has to be loaded interactively to make that work and I think the default is to load it via DelayedLogic for performance reasons. That's why you might have seen the need to reload your page.

When I remember it correctly, does this solution not work if you are using an application server connection. In regards to the web portal, the object has to be loaded interactively to make that work and I think the default is to load it via DelayedLogic for performance reasons. That's why you might have seen the need to reload your page.