There is an Xposed Framework module called App Settings that will allow you to change the DPI for apps on an individual basis. Also lets you change the app layout eg phone, phablet, tablet.
I think if you change the DPI for "Android System" it will change it across the board.
It's like PA's Hybrid Settings, but not as pretty to look at when using.
Nexus 10 - STG7
Galaxy Nexus - Simbean 4.2.1 Beta 1