Make a bootable USB Flash in Linux - with Grub or another one

I have two USB Flash . A USB flash load software after Linux boot and other USB Flash load other software on MS -Dos, I would like to merge the two into a single USB flash and when the boot starts must appear which one I desire to boot ( and when we done the project, We can also change the boot sequence when we needed , either by Grub - text file or any boot system that you use in this project ) . For those who want to examine one of the USB Flash follows the download link : [login to view URL] Note: This first USB Flash consists of two partitions: * The smallest partition we have all the settings that the software / game saves in xml file format. * The second partition (the largest one ) is in raw data format ( 0x83 ) . We need access to the files of the structure of this USB flash to boot and edit the Grub file, but we have to get ready after the project to maintain its current format ( files hidden or inaccessible configuration, creating a certain difficulty in access or changes in structure of the boot, like is already done in the second partition -raw data format ) . In short , we have to have information to allow us access, just to change the boot and protect it in the same pattern again.