Notice of Filing and Immediate Effectiveness of a Proposed Rule Change To Amend Interpretation and Policy .13 (Temporary Extension of the Limited Period for Registered Persons To Function as Principals) to Exchange Rule 1900, Registration Requirements, To Extend the Expiration Date of the Temporary Amendment Set Forth in SR-EMERALD-2020-21 From April 30, 2021 to June 30, 2021