Computed RichText Item

Guys, I have a requirement wherein a particular rich text item is initially editable, then it must be non editable once the document is processed. Note that when I said process, the document underwent to several processes and some fields are still editable except for that rich text field. My question is what are the other posible ways to control that access in that rich text bssides to put it in the controlled access section or create a new computed rich text field that will duplicate the content of the editable rich text. But I doubt the later one is good since it will only double the size of my document.

Thanks for the suggestions

Subject: two computed subforms

using just one - sometimes the one with the editable field, somtimes the other one.