The Scrum Team membership should change as needed, but not too frequently, as it may affect the team’s ability to deliver value and maintain a high level of collaboration and self-organization. The Scrum Guide states that "Optimal Development Team size is small enough to remain nimble and large enough to complete significant work within a Sprint. Fewer than three Development Team members decrease interaction and results in smaller productivity gains. Having more than nine members requires too much coordination. Large Development Teams generate too much complexity for an empirical process to be useful."1 Therefore, the Scrum Team should consider the impact of changing its membership on its productivity and performance, and balance the need for stability and flexibility.

References:

1: The Scrum Guide2, page 6

2: The Scrum Guide