Along the lines of this thread Can Biden re-hire someone Trump has fired?, can Biden sign a single executive order that undoes every executive order signed by Trump?
Not bloody likely he would but wondering if it could be done that way. Something like:
Every executive order signed by former President Trump is revoked.
Biden
President of the US
No. Self-evident proof: if it were possible to do so, Trump would have done that with “Obama” on day one.
There’s a process that changes to various administrative rules have to go through, legally. Several of Trump’s initial attempted executive orders failed because they failed to legally follow that process.
!. Trump may not have figured it out.
2. Doing it piecemeal kept him in the news.
Even if he could, one of them would be the federal civil service pay raise from the end of 2019; I don’t think Biden wants to undo that. Also, would it mean that the holiday Trump declared on Christmas Eve in 2019 would be revoked, and every federal employee at the time would be docked a day’s worth of annual leave (“vacation time”)?
I don’t think a executive order can turn back time, the authorization for the day off would be gone, but the day was still off in that respect by virtue of the spacetime continuum, but you bring up some interesting lingering chaos from the removal of Trump.
To put a finer point on the OP, can Biden selectively revoke Trump’s Executive Orders? For example, can Biden pick one, and cancel/revoke/undo/reverse it? Like Executive Order 13769 (the “Muslim Ban”).
It depends on the order. Biden can’t “unpardon” anybody that Trump pardoned, presumably under the “double jeopardy” clause of the Fifth Amendment, but for laws that Trump modified through executive order, Biden would have the same authority to modify the same laws.
It may be possible Why It Might Be Impossible To Overturn A Presidential Pardon | FiveThirtyEight.
As for double jeopardy I don’t think that would apply as a pardon does not reverse a conviction, just the punishment. The person still has a conviction on their record.
It seems like this thread is conflating different types of executive actions, each of which has its own requirements and limitations.
An executive order is a directive from the President to some element of the federal bureaucracy to execute their duties in a particular way. The order cannot conflict with statute requirements or formally-adopted rules. Executive orders derive their authority from the President’s discretion to determine how the executive branch will prioritize and enforce laws absent more specific directives in statute or rule. Any president can issue, modify, or cancel any executive order at any time, including those issued by his predecessors. However an EO is still subject to challenge and judicial review should it contravene the Constitution or statute.
A rule is issued by an executive agency through a formal process outlined in the Administrative Procedure Act. Agencies may adopt rules where Congress has delegated them authority to do so. Generally, Congress will outline goals and requirements for some administrative action, and leave it to the agency to adopt the specific details of the action through rulemaking. Once adopted, a rule can only be repealed or modified through a subsequent rulemaking process, or an act of Congress.
The pardon is an explicit Constitutional authority of the President. He can exercise it anytime, anywhere and on anybody, within some very broad limits that have been recognized by the Supreme Court (e.g. the President cannot pardon future crimes). Once issued, a pardon cannot be revoked. Whether a President can self-pardon is the subject of much debate these days, but has never been tested in the courts.
Yes.
Joe Biden isn’t going to be pressuring government lawyers to break the law the way Trump pressures White House staff (and his tax preparers).
I consider this good. I am against what we used to call the imperial presidency (of which the Trump administration is a 10X version).
I don’t know the answer to your question. But I would just say that I wouldn’t advise it, were I Ron Klain or some other top level Biden appointee. I can see the Republicans now claiming how the new president wants to start ruling by kingly fiat on day one. Even so, I would love it if it were possible. 
Moreover, such an action would go directly to the Supreme Court, which at present wouldn’t look kindly at sweeping quasi-legal actions by Biden.
Besides, the notion of being able to do so implies just as sweeping ignorance of how an executive order reads. You can find the 2020 ones here. Click on any pdf. They’re filled with references, terms, definitions, and pages of legalese spelling out exactly what is being changed, just like a congressional bill. I don’t believe they can be reset like an odometer. Careful attention needs to be paid just to re-establish the policies that previously existed, because other changes may have been done in the interim created other than by executive order.
The Office of Counsel to the President and Vice President has more than two dozen lawyers attached to it. They’ll all need to be working full time to parse out the details of Trump’s 192 orders. But they won’t have time, since they have a million other laws to contend with. Reversing the executive orders will be a slow and piecemeal process.
Trump attempted to reverse Obama’s EO that created DACA. He failed to jump through all the proper hoops and SCOTUS disallowed that. I think he is still trying again, but Biden will nix that.