Not advice, just info. When you enter on a certain visa class, you have to abide by the visa class. If you enter on a J-1 and you are permitted to stay to a certain date, you need to leave by that date (plus any grace periods). If you reenter on a different visa, you then have to abide by that visa. The wild card is CBP, which is the final arbiter of whether you are permitted to enter the country. If the officer believes that you are circumventing the visa process or will not abide by the terms of the visa, they have the right to refuse entry.

Bottom line is that there are many people with multiple visas and multiple visa classes. It is their responsibility to know the terms of the visa on which they were admitted and to adhere to the terms. You can consult with your lawyer, mother or priest, but in the end you are the one responsible for your visa.