He could only do that if Congress authorized it … and even then there was no legal authority for them to do anything other than ask the legislature for clarification.
Once the electors were certified on December 14th there was no way to change them. That’s why any action taken by a state legislature had to be done BEFORE that date.
What would have happened if (for example) Pennsylvania’s legislature had voted to certify the Trump electors on January 8th? This would have been subject to multiple court challenges even in PA state courts — without even any consideration for Federal court challenges.
The 1877 Act did not limit the VP’s role only to something ceremonial, but instead, established a procedure for handling competing electors from each state.
The Act established a special Electoral Commission with fifteen members, including five members from the Senate, five members from the House, and five Supreme Court Justices.
Pence could have arguably sent disputed electors to that Commission. Instead, he acted as if he had no authority to do anything.