Can a senior rater have influence on rater's comments? How can a service member appeal what he/she was rated has ?

First, evaluations should be an ongoing team effort involving ALL parties and really should be a roll-up your quarterly counseling sessions with input from the NCOER support form. If there is disagreement between the raters, then that indicates a problem with the evaluation process throughout the rating period.

As you know, the rater will provide the meat of the evaluation and should have on hand the documentation and facts needed to support the bullet comments. The senior rater can have influence but really should not force a rater to make changes to the comments unless those comments are verifiably incorrect. For example, if you have a negative bullet because a Soldier is consistently late and takes extra effort find motivation to do the job, that behavior should have been addressed and documented with a DA 4856. If the senior rater wants you to give the soldier a break and give a kinder evaluation, and you have the documentation to support the negative bullet, then you should stick with your guns. It may take senior leadership involvement to resolve this issue.

As far as appeals go..refer to AR 623-205 (chapter 4 and appendix F). It contains all of the policies and procedures that need to be followed. Requests must contain, as a minimum, a memorandum from the NCO, a copy of the report in question, and supporting documentation. All documents submitted that are not on the NCO’s OMPF or are not an original copy, must be certified.

Yes,
But its up to the Rater to capture the picture and if the SR has seen something that he/she missed then they can bring it to the attention of the Rater.

Okay, assume I am the senior rater. That means I probably rate the rater.
Enough said. Of course I would have influence.

Now would I try to use it to have the rater do other than he/she sees as right. No, I wouldn't. But, I speak only for myself.