About Defintion of Done

I have some questions about DoD:

Context: Imagine that you are developing a Product during 7 Sprint, all is going well on Reviews but during Sprint 8 your PO says to you (as Scrum Master) that de Product has performance problems. Questions:

• Can you change DoD during the Sprint to avoid accumulating waste avoiding to wait for Retrospective?
• Is it better that team waits for Retrospective meeting?
• Can the PO bring the performance concerns to the Development Team directly during the Sprint? 

Thanks