Well, considering the nature of that command there is always some risk. Be sure there are no typos and try to understand what you are doing before you hit the enter key.
There is a visual example above my post on page 3, though he already knew which partition he was booting from. You need to be logged in to see any uploaded images or files on this forum.
It's always best to have a usb to tty serial cable such as Adafruit 954 available just in case you run into problems. You can always flash from u-boot environment with TFTP and this cable.
Remember, you cannot simply flash what you have downloaded directly from Linksys. It needs to be converted into a flat file. Luckily this has already been done for you; see my posts on page 3 or page 4.
Also, the venom.img that is offered on page 1 will not match what you currently have on your router. It is not official Linksys firmware, but compiled from GPL source.