Yes. When the patentee would like to reduce the number of claims for issued patents, it is possible to file “Application for Registration of Partial Abandonment of Patent Rights.” In order to take such a procedure, a “Partial Abandonment of Patent Rights” and a Power of Attorney signed by the patentee are required.
No. It is not possible to substantively amend claims after payment of the registration fee. Only cancellation of claims, correction of typos, and narrowing scope of claims are allowed after issuance of a patent.
It is necessary to file an “Appeal for Correction” together with corrected claims and specification. A Power of Attorney also is required.