There is usually a piece of software running on the machine which basically just does this - allows you to command an image upload to the SSD, do a checksum of the file, then install it if all goes well. There is also usually a simpler version of the software on a redundant SSD or partition which the onboard computer will install if it detects that the software that is currently installed is malfunctioning.

My understanding is that some spacecraft launch with beta/alpha equivalent software. Correct me if I'm wrong, but I believe that the rovers do this, with simple software installed first, then more complicated versions installed once they know everything is working.

It's somewhat similar to updating your iphone, but instead you use a huge dish to do the transmission and the bitrate is pretty horrendous.

I'm going to need a definition of "ad-hoc" here; no-one "deploys straight to production" on a spacecraft. Any patches have to be thoroughly tested on simulators and models of the spacecraft on earth before they are transmitted.