Well 2012 is compatible with 2010, i am not sure this would work but i found this on how to go back from 2010 to 2008, hope it works for you with 2012 (Original Link):
Make back up of your .sln file
Open your VS 2010 .sln in notepad.
It should look something like this:
Microsoft Visual Studio Solution File, Format Version 11.00 # Visual Studio 2010 Project("{FAE04EC0-3 ......
Change the Version 11.0 to Version 10.0 and the Visual Studio 2010 to 2008
It should look something like this:
Microsoft Visual Studio Solution File, Format Version 10.00 # Visual Studio 2008 Project("{FAE04EC0-3 .....