If you added a column and you want to revert back, you just drop the column again! What's so hard about that? No 'migration' needed.
In BASIC you can 'declare' a variable by simply using it. The compiler will not warn you if you use an undeclared variable. That's the analogous situation here.
In BASIC you can 'declare' a variable by simply using it. The compiler will not warn you if you use an undeclared variable. That's the analogous situation here.