ok i forgot to mention, that I am a total noob in scripting or BASH. And sorry for my bad English, in german it would be easier to explain.
I think a startable scriptfile is the best solution for my problem.
I have a GTX 970 (no EFI), which I use with the Yosemite-System. Unfortunately I need for some programs Mavericks, which I use with my Radeon HD 5770. With the non-EFI card i dont have the boot-screen, so i cant choose the bootvolume. Also i have to deactivate the NVIDIA-Driver if I want to boot in Mavericks or I get the bootloop (http://forums.macrumors.com/threads/frequently-asked-questions-about-nvidia-pc-n on-efi-graphics-cards.1440150/). So the best solution is a script in my dock, which deactivates/activates the driver, sets the startvolume und reboots, if I want the change the system. I think this script goes in the right direction:
do shell script "bless -mount /Volumes/Name_of_the_other_SSD" -setBoot password "xxxxxx" with administrator privileges
do shell script "sudo nvram boot-args="nv_disable=1"" password "xxxxxx" with administrator privileges
tell application "System Events" to shut down
But once again, Im a total noob, so I dont know what put in the Path-String for the right SSD....