There are two issues: Tense agreement and construction of a conditional.
The first sentence is not correct because there is not tense agreement between the verbs “did...change” (past tense) and “have” (present).
A second reason is that the construction “How...if...” calls for a conditional, so “would” is a better auxiliary than “did.”
English is remarkably plastic. One can wrench many seemingly ungrammatical statements into line by providing suitable context or by specifying an unusual point of view.
In your fellow-teacher’s example, we could posit this hypothetical context:
he (or any pronoun you prefer) is as rich as Bill Gates, and has been for a long time;
he experienced a ...
It is generally used to defend one thing by comparing it to the other. The specifics depend on context. One would need to either know what the comparison is from common use and knowledge of the situation, or it would need to be specifically explained in the essay.
For the example you ask about, in the USA the context is that alcohol is legal (with ...
"just because I think something is good and proper and nifty you don’t necessarily have to.” =
"just because I think something is good and proper and nifty, it is not necessary for you to [think something is good and proper and nifty]."
If you put a comma after nifty, it creates a pause that might help with comprehension:
"... just because I think something is good and proper and nifty, you don't necessarily have to [think that as well]"
Grammatically, you have:
you do not (second person negative of "do")
have to (+ omitted verb/verb phrase) (modal verb of ...