It's probably a mistake to read a lot about the subjunctive mood in English, because English doesn't have a subjunctive mood. This may explain some of your confusion.
What English does have is some funny uses of a few words like was and were in idioms like
if I were you (which means, roughly, 'my unsolicited advice follows')
normally occurs at the beginning of a sentence. Advice may be formulated in the first person
if I was you is considered substandard, because were is completely frozen into the idiomIf I were you, I would keep my mouth shut about this.
if it was me (which means, roughly, 'my unsolicited reaction to this would be: ')
if it were me is equivalent and is identical in meaning and usage.
... though the were variant may falute slightly higher to some people.were it not for
X
(which means 'ifX
was not the case', and presupposes thatX
is the case)
was it not forX
is ungrammatical -- not just substandard -- because the initial were is necessary in order to recognize the idiomatic clause structure and parse it correctly.
These are common, which is why they're frozen, and they're idioms, which means they don't follow normal rules. They often do follow other rules, however, which have died out in the language. But zombie rules isare not usually helpful things to read a lot about; for one thing, they're full of holes.