Can a collaborator edit only some rooms of a tour?

No. A role applies to the whole tour: an Editor can change every room of it, and a Viewer none. What you can choose is which tabs each role opens, under Client Workspaces in My Account: for example Editors who open the Hotspots tab but not Panoramas.

To keep some rooms out of someone's reach, put those rooms in a separate tour and invite them to that tour only. Invite collaborators to a tour and set their role has the roles.