How to Allow users edit their own messages (including guest) but not delete messages or channels

Hello, yes it's possible to set both members of the team and guests to only be able to edit their sent messages. Member permissions (many) and guest permissions (few) are set under the team settings including the permission "Give members the option to delete their messages" for example, and in the Teams admin center you have the Org-wide Guest access settings which includes the option "Delete sent messages". When it comes to the permissions for deletion of channels these are set under the team settings for both members and guests.

Let me add that you can also use a messaging policy with "AllowUserDeleteMessage" if that is something you would like to use and the https://docs.microsoft.com/en-us/powershell/module/teams/set-team?view=teams-ps