I know someone in NM that runs them front and rear with no issues and does not carry his normal tags with him. He even has is sticker on them.
2001 Focus ZX3 Race Car in Germany-Ours
2010 Renault Clio 1.2 16V in Germany-Hers
2004 SVTF EAP/ST170-Mine
2013 Focus ST2 TS NAV SUNROOF-Hers