For instance, for reasons that I am not clear on, it seems that every (Yaesu) radio programming tool requires that a cloned image be made of the radio, then updated, then sent back to the radio. If I mess up this image and send it back to the radio, can I render the radio useless?
The short answer is: no, you won't brick the radio.
The long answer is: I've never bricked a radio and I've sent them all manner of broken stuff. You're not uploading firmware, you're just uploading a map of the memory channel data (and other settings). Icom radios are very good at sanity-checking the image and reporting error at the end (and then resetting). Yaesu radios (as in many areas) are far less careful and will often accept any image you send that is in the right format and size. The worst I've ever seen is when you boot the radio back up, the internal firmware reads some of your garbage and does something weird (potentially locking up, but that's very rare). Pulling the battery and doing a key sequence to reset memory on power on always clears that out.
So, I can't make any promises, but I highly recommend you not worry about bricking it :)