you need to do research.Government is not set up so that every necessary change has to go back to the legislature. They often have provisions giving those implementing the law power to make rules meeting new situations.
The Georgia response to the Texas case describes the authority of the State Elections Board to make changes and explains those changes. This authority was provided by the state legislature:
"Under Georgia law, the State Elections Board has authority “[t]o formulate, adopt, and promulgate such rules and regulations . . . as will be conducive to the fair, legal, and orderly conduct of primaries and elections” so long as those rules are “consistent with law.” O.C.G.A. 21-2-31(2). The State Elections Board exercised that statutory authority by adopting State Rule 183-1-14-0.9-.15. Indeed, a different statute—O.C.G.A. § 21-2-386—allows the State Elections Board to preliminarily review absentee ballots before Election Day, and expressly provides the county election superintendent with “discretion” to tabulate ballots prior to the close of the polls even in regular times."
https://www.supremecourt.gov/Docket...0145849997_Georgia -- Brief in Opposition.pdf
In Pa for example the Republican legislature DID change the rules for absentees to be accepted up to election day.
The Sec of state -thru the courts changed it to 3 days after - he had already gone to the legislature to try for an extension and they turned it down
The Supreme Court of PA had absolutely no business getting involved;all plenary power to set terms of the election belong to the Legislature