What is so difficult to understand?
Any law, including sales tax, can be changed anytime by simple majority vote just like any other law (senate filibuster may or may not help a bit)
It is meaningless what protections you write in to the law. What congress passes, can be changed if (future) congress and president so want.
To change a law requires both houses and a Presidential signature, or veto override in both houses.
It’s really elemental. Just read the constitution or look up School House Rock on how a bill becomes a law.