Would a survey immediately following an accredited CE activity that asks specific practice change questions be sufficient to measure changes in learners’ performance?

No.  Changes in performance may only be assessed once a learner has had an opportunity to implement changes in their practice, so assessing performance change immediately post activity is not appropriate.  However, self-reported changes in performance collected several weeks or months after learners have had an opportunity to implement what they learned into their practice would be an appropriate measure of performance.