Below is a useful maintenance mode tool for SCOM 2012, it is a gui that you can use to put SCOM monitored Windows and Linux computers into and out of maintenance mode.
Just copy all the files (including the 3 dll files) into the same folder and run MMTool.exe
NOTE:-You cannot use this tool to schedule maintenance mode for a later date, it can only be used for real time maintenance mode but it means users can put servers into maintenance mode without using the SCOM console.
If you are looking for a tool that you can use to schedule maintenance mode for a later time or date there is a tool that you can use but it isn’t free, you can find it here:-
http://www.scom2k7.com/scom-2012-maintenance-mode-scheduler/
Scompanion 