Special Values on Text Questions

Is there a way to add special values to a text question? I know this can be done with numeric questions, but have not found a way to do this with text questions.

For some context: I am creating a survey in which respondents will be asked an Open-ended question (programmed as a text question), but I also want to have Don’t know and Refused response options available for the interviewer to select:

Q1: What is your opinion on topic X? [Open-ended]
98 Don’t know
99 Refused

Use a 2 question combination, with 1st categorical, your categories above plus 1 answer given, then if 1 activate the text 2nd text question for the answer itself.