Is "irrespective of" interchangeable with "regardless of"?

I would refer to an insightful essay entitled "Regardless v. Irrespective; Regard v. Respect". Lauren, the author, introduces herself as a defense litigator and writes that "In law, we are taught that there are no true synonyms." ¹

Regardless has the idea of ignoring something to which you should have paid attention, while irrespective is dismissing something to which you had no need to pay attention.

The full essay has more examples, etymology, and detailed reasoning.

No. You could certainly use 'irrespective' in that last sentence. It is difficult to think of an example where they would not be interchangeable. Being such a hybrid language which draws vocabulary from a range of sources Anglo-Saxon, Norman French, Latin, Greek etc, English does have an immense vocabulary, which gives you the opportunity to interchange words which makes your writing more enjoyable to read. In this example both words originate from Latin. But if you take pig and pork, or cow and beef, or sheep and mutton, one word in each case is Saxon, the other Norman French. There are multitudinous examples of this kind.