@Lyndon ***********
, If it's a single entry visa, it will be used and not valid anymore when you entered on that visa.
If you have a multiple entry visa, it is valid until it's expired. You don't need a re-entry permit for a multiple entry visa because it has unlimited entries as it says "multiple entry". (Or a re-entry permit from the immigration office inside Thailand is meaningless for a valid multiple entry visa.)
Visa (old-style sticker or eVisa) itself cannot be canceled.