Can I apply for marriage green card in RPI status?

Typically the way the United States immigration laws work is that you can file multiple immigration petitions to USCIS and then take advantage of whatever petition is approved first.  You can then simply withdraw the remaining petitions.  This liberty provided to the immigrants allows them to diversify their risk and hopefully get approved faster.  Unfortunately in the Border Security, Economic Opportunity, and Immigration Modernization Act of 2013 (BSEOIM), if an undocumented alien applies to adjust status to Registered Provisional Immigrant (RPI), for the duration of that status (5 years for the DREAMers who entered the US before the age of 16 and then 10 years for all others), he of she cannot take advantage of other paths.  For example, an undocumented alien who applies for RPI and is either while the approval is pending or has been granted, gets married to a US citizen and is eligible for adjustment to permanent resident status, will not be able to do so.

While the RPI legal status gives an alien all the privileges of a green card except the permanency, but it appears that the law aims to keep its promise that anyone who entered illegally or is in unlawful status cannot be given LPR status before all others who are waiting in line.  In the same spirit, if you already have an immigration petition pending before USCIS and you file your RPI application as well, but the previous petition is approved first, you get to take advantage of that and simply withdraw your RPI petition.