From Microsoft 365 Copilot, you add custom instructions.

The instructions will apply to new chat conversations.

Answer: Yes

The instructions will apply to new conversations with the Researcher agent and the Analyst agent.

Answer: Yes

The instructions will apply to previous responses in existing conversation.

Answer: No

Custom instructions in Microsoft 365 Copilot are a persistent preference mechanism that influences how Copilot responds going forward. Once configured, they are applied when you start new interactions, helping Copilot maintain consistent tone, formatting, and behavioral preferences across future chats. Therefore, they apply to new chat conversations (Statement 1 = Yes).

Custom instructions also carry into new conversations you initiate with Copilot experiences and agents (such as Researcher and Analyst), because the instructions act as a user-level guidance layer that shapes responses regardless of which Copilot “mode” you start—provided those agents are being used in the same Copilot environment and are subject to your settings (Statement 2 = Yes).

However, custom instructions do not retroactively change content that was already generated. Existing conversation history and any prior responses remain unchanged; the instructions affect subsequent turns or new threads, not previously produced outputs (Statement 3 = No).