No such guarantee would be meaningful if the US administration and congress change their opinion. Whatever they write in law or sign, they can undo -- if not legally then in practice.
- The US had ratified a treaty with Panama about who had control over which part of the Canal zone, yet they deposed Noriega.
- The US had given security guarantees to Ukraine when Ukraine surrendered their nuclear weapons, and then failed to follow them.
- The US had made a deal with Gaddafi to make him drop his WMD programs and then supported his overthrow.
- For that matter, the US had made a deal with Iran on nuclear issues and it is generally understood that Iran held that promise, yet the US broke the deal.
The only way for another country to be safe would be to join another strong alliance, or to retain sufficient military leverage to make an US attack unlikely.
On the other hand, US foreign policy doesn't have to "change drastically" when the administration changes. Johnson and Nixon both fought the Vietnam war, Bush and Obama fought the Iraq counterinsurgency, and so on.