No, screener questions can't be added once a study is live. But if your study is still in review, you can still edit it: use Revert to draft from the menu in the study header, make your changes, and resubmit.
Why live studies are locked
Applicants who already applied never saw your new question, so there'd be no data to show for them in the participant list, and recruitment that's already underway can't be re-filtered retroactively. Once a study is approved, recruitment settings (screener, audience, quota) are locked.
Still in review? Edit it now
Open your study.
Add or edit your screener questions.
Resubmit for review.
My study is already live. What are my options?
Ask existing applicants in a message. Bulk message participants with the question and read answers from the chat. It's manual and not everyone replies, but it works for a single follow-up question.
Run a fresh study. If the missing question changes who you should be recruiting, a new study lets us recruit cleanly against the right criteria. Talk to us on live chat first; depending on the situation we can help with how credits carry over.
Make the screener count next time
Closed-choice questions (multiple choice with clear qualify and disqualify options) actively filter recruitment. Open-text questions can't, because there's no answer for the system to match against, so they shouldn't carry your must-have criteria. If recruitment is pulling the wrong people, this is the first thing we check. See I need more participants.