There are not really any "rights'" based on your certification. What you do have is common sense for correcting minor errors. If the wrong Preventive E/M was circled due to the patient's age, correct it. That does not change what happened in the visit, it is a minor correction.
Whether or not to make corrections on missing procedure codes depends on what they are. If you see in a note they gave an injection but it wasn't circled, then circle it. Or if there is a test that was done, like urinalysis, pregnancy test, glucose test, hematocrit, etc. same thing. These are items you can clearly see in the note were provided, just left off the billing form.
If you have a superbill that has incorrect procedures circled, or missing more than just a minor procedure code, that probably should go back to the provider for clarification. This would be a good time to get in writing a policy and procedure for dealing with these situations.
Remember, superbills are just a tool used to communicate information regarding what happened in the encounter. A corrected superbill is not documentation and is not used in an audit situation, so changes made to a superbill would not need official letters of explanation. As long as what is billed to the insurance accurately reflects what is in the encounter notes you are covered in an audit situation.