once you apply for your GC, and you change your employer, after your LC is approved, it doenst matter as much, if your new position at your new employer is consistent with your previous employer, and stated in your LC, as long as your new employer is willing to sponsor you too. For national interest waiver, there are certian criteria USCIS follow , now you decide on your own if your job fits in any of these. The aliens admission will improve the U.S. economy. The aliens admission will improve wages and working conditions of U.S. Workers. The aliens admission will improve educational and training programs for U.S. children and underqualified workers. The aliens admission will provide more affordable housing for young, aged, or poor U.S. residents. The aliens admission will improve the U.S. environment and lead to more productive use of the national resources. The aliens admission is requested by an interested U.S. government agency. my suggestion, use the regular LC way. but consult your own lawyer. goodluck.