For an executive order to be unconstitutional, it has to be in conflict with existing federal law. For example, if a president issued an executive order making changes to Medicare reimbursement forms for providers or to increase regulatory oversight of Medicare Advantage providers, then it would most likely not be in conflict with existing federal law and thus not unconstitutional.
However, if a president were to issue an executive order instructing Medicare Part D to start using its purchasing power to negotiate lower prices from drug companies, that would be clearly in conflict with existing federal law. Thus it would unconstitutional and would successfully challenged in the courts.
To start a thread that gives some hypothetical example of an executive order that hasn't even been issued and then predict it could lead to future executive orders of some future administration is useless conjecture.