Yes, Existing assessees can amend the details whenever required by filling in the details in the application again. New assessees can also amend the registration details after approval of Physical Verification report by the AC/DC. In certain cases (like change in constitution of business), the details changed may warrant a fresh physical verification or the issue of a new Registration Certificate..
You can submit online request for surrendering your Registration Certificate in ACES though:
REG-> Surrender RC (In case of CE)
REG->Surrender (In case of ST)
Once the surrender request is submitted by the Assessee, approval process passes through the Superintendent and then AC/DC.
The word "Person" shall include any company or association or body of individuals, whether incorporated or not. Thus, this expression includes any individual, HUF, proprietary firm or partnership firm, company, trust, institution, society etc..
There is no need to file A1 form again. There is a provision in ACES where Assistant Commissioner (AC) or Deputy Commissioner (DC) will re-assign your application to correct jurisdiction. You can contact the jurisdictional officer if required.