It is not possible to change directly
from field1 = 1 and field2 = 0
to field 1 = 0 and field2 = 1

That would cause field1 to fail validation since during that change field1 is 0 and field2 is also 0. Once you change field2 to 1 field2 should validate but field1 will not revalidate unless it's changed again. Basically there's not validation chaining as that'd just cause the fields to get stuck in a loop revalidating one another.