Use the Subscribe/Unsubscribe feature to indicate whether a stakeholder is happy to be contacted by your team. Mark them as Unsubscribed if they no longer want to be contacted:
Open the stakeholders' record page
Use the button at the top right hand corner of the record page (above the stakeholder's name) to toggle between Subscribed and Unsubscribed.
You will also find buttons here to indicate the stakeholder as Inactive/Active.
If a stakeholder record is marked as Inactive then your team will not be able to edit the details on the record page.
Note: Marking a Stakeholder as Unsubscribed can not prevent your team from contacting them - it is an indicator only.