If my tomorrow is being your yesterday = If my tomorrow is your yesterday?

It seems to me that "is being" is actually incorrect here. If my tomorrow is your yesterday is in Simple Present, whereas it is also possible to put the sentence in a subjunctive mood, ie. If my tomorrow were your yesterday or even If my tomorrow be your yesterday, which sounds more poetic and old-ish.

That said, I doubt that If my tomorrow is being your yesterday is even grammatically correct, although it is clear it wants to express the same thing as If my tomorrow is your yesterday.