[linux-audio-user] sysex questions

Hi, I'm having some silly questions, I'm new to the midi world: I just bought a Boss GT-8 guitar effects processor and I know it supports downloading patches to your computer. I understand this works over midi by doing a sysex dump. What I don't understand is: How does the program I use "know" what kind of data I download? A patch? The system configuration? Everything? I know it does not need to be able to interpret the contents of those things but I'm not quite sure how this stuff works at all. And the other way round: Could I do any harm to my GT-8 (or another midi device) by uploading wrong data to it? Or will it just give me an error message and reject the upload? What programs can I use under linux? I know sysexxer, but I would rather like to use a command line tool. As I said, silly questions