PL0049: Variable has type that does not support protection

I would like to protect preloaded data in a TEXT question type. When I try to create assignments using batch upload I get the error " PL0049: Variable has type that does not support protection." I have read the articles at Protecting pre-loaded answers and Design limitations by question type.

Is what I am trying to do possible, and if so, how?

The first article says: “The protection applies to questions that may perform the role of triggers”.

TEXT type question may not be a trigger hence can’t be protected.

What is your survey story?/context?

I have a listing roster in which one of the questions is about the category of building and one of the options is “other (specify)”. There is a follow-up question to collect this. In the current survey, the category of building is an identifying variable. I want to display the other building category but it does not have to be identifying so I made it a Text interviewer question that I would like to preload with the collected answer.

Make it a text hidden variable and preload it.
Use text substitution to show it in a static text.
Hidden questions can’t be changed by anyone, once they are preloaded.

This worked well. Thanks.