Are you looking for loopholes?
First of all, the Oxford comma is a rule about punctuation, not grammar.
Secondly, there is no official rule-making body for English along the lines of the Académie française for French. What English does have is a long history of towering literary geniuses living alongside a group of tiresome scolds. The former teach us the rules from the beacons we keep on library shelves, and the latter hector schoolchildren held captive in classrooms.
Thirdly, English is notorious for having exceptions to general rules:
- Adjectives precede the noun they modify: a red ball, not a ball red.
But attorney general and court martial. Channing Pollock wrote a
play called The House Beautiful, famously reviewed by Dorothy
Parker as "the play lousy."
- Pronouns are placed in the objective case when they're objects; nominative case, when they're subjects. But only the pretentious say
"It is I" instead of "It's me." And "whom" has all but disappeared,
especially in conversational English.
- The subjunctive is supposed to be used for uncertain conditions or
conditions contrary to fact, but it's been supplanted by the
indicative in most tenses. Have you heard anyone say, "If I be late,
then start without me"?
- I am; you are; he is. I'm right, aren't I? Check the google and you'll finds reams of reasons why "aren't" is just fine as a stand-in
for the missing "amn't."
And then there the rules that aren't really rules -- don't end a sentence with a prepositon; don't start a sentence with a conjunction; don't split infinitives.