Multiagent Systems are potential computational systems for various practical applications, tools, and so on. Multiagent simulation is one of the remarkable application to evaluate several kinds of phenomena. In order to design an agent for multiagent simulation, it is important to reflect user's opinion. However, if a user is not computer professional or does not have technical knowledge of agent logics and programming language, it is hard for him/her to implement his/her own opinion. Participatory design is a promising approach to incorporate user's opinion in the agent design and modification process. In this paper, we propose rehearsal oriented testing for implementation of participatory design. By the rehearsal oriented testing, it becomes possible to carry out anytime modification of agent's scenario, which describe its behavior during simulation. For rehearsal oriented testing, we set operators for modifying scenarios, which is described using finite state machine model. We also design interaction protocol between a user and an agent to smoothly get information through the user-agent dialog for modifying operators. Under this protocol, an agent informs a user about what kind of information is required.