How is it possible to make a TextBox in Presentation readonly with an variable Value?
I don't think it's possible to do it with the current vCO versions. We have such property/decorator, named 'Editable', but it is not exposed in the presentation editor UI. Not sure why.
Consider open a support request if you really need it, and we'll evaluate it for inclusion in the future vCO version.
I could use that, too, although it's not blocking us right now, just a UI annoyance in the form.