In the new Assessment tool, question types cannot be changed after the question is saved.
Learning Management System
Changing after saving is supported only in legacy PQE and was never supported in Assessments. In Assessments, changing the Question Type was only supported in Quizzes, and that too only before the newly added question is saved. Assessments is a new tool and implements a different flow and also changing the question type is not a core functionality.
In this case, if you feel that there is a strong business need for a change on system functionality, such request should be raised as an enhancement request in the SuccessFactors community. The following note explains how you may raise such request:
2167560 - How to submit an Enhancement Request for SAP LMS
Quizz, cannot change question type, assessment builder , KBA , LOD-SF-LMS-ASB , Assessment Builder , Product Enhancement