Yotta toolchain - bootloader?

I am trying to setup a toolchain to compile my project with Yotta (target: nrf51dk)
The project compiled successfully and I see both the hex files and a “XXX-combined.hex” file, which I assume, has the softdevice inside.
How can I choose which softdevice is selected, and how can I add to merge the bootloader into the combined file as part of this toolchain?

Nevermind. Found it. IT is under /targets/nordic-nrf51822-gcc/CMake/toolchain.cmake