It's not a case of trying to change the rules it's simply that the description doesn't fit. MMT came about as a descriptor of the US system, its subsequently been found to apply in other countries with similar characteristics like Canada, UK and Japan. One of the reasons that these countries can always create money to pay debt liabilities is because all their debt is denominated in their own currency. Thats not the case in Argentina and thats why the model doesn't fit.
MMT doesn't say anything about what we should do now! I think an understanding of MMT changes the narrative and makes different policy choices possible. It doesn't however answer political questions or prescribe policy. It just explains how money works.
It's a fallacy.