Moving permissions to optional on chrome extension

I learned about Chrome disabling an extension when new permissions are added the hard way.

When I add new features to my extension I need to add new sites in the permissions list. Now I know I should have used optional_permissions.

My questions are:

1. If I move the site's list from permissions to optional_permissions does the user need to approve those sites again? or just the ones that I add over time.

2. Could any of these changes cause the extension to be disabled?:

   a. I add sites in the matches section of an entry in content_scripts

   b. I add sites in the matches section of an entry in externally_connectable

3. Is there a way to define externally_connectable in optional_permissions?

Related links: chrome.permissions | Permission Warnings

Update: When Chrome disabled my extension I had added in the manifest one site on content_scripts > matches and externally_connectable with a matches site. The latter shows a new line in the permissions warnings saying "Communicate with cooperating websites". I'm not sure which change caused the disabling, that's why I ask about externally_connectable too.