As far as I know there is nothing in the boot rom that checks signatures, it just jumps to the correct location in flash (10000 I think) and starts executing from there. I guess the big things to make sure of are that you don't write to areas of flash or memory mapped hardware accidentally, as it would be a shame if you overwrote the boot area of the flash (assuming it isn't potected) as then you couldn't even put an Empeg image back on.