I called the USCIS about the I-539 because I found the TN instructions unclear. I was told that yes, you can use that form to apply to change your status from TN to B-2 visitor.
I forked over the $300 (a hard thing to do since I can't collect UI benefits and need to save for COBRA -- sorry, I digress) because I am getting medical treatment and the round trip would be difficult. But as Steven says, if you're at or near a border, leave and re-enter there, if only to save the money from filing the form.



