Philip,
I have not done it in a long time, renaming captured images, however if you are unable to right click the name in media manager and rename them there, then you probably will have to rename them the way I did long ago.
I captured all the images and saved them to the USB connected to the switcher, then I took the USB stick to a computer and renamed all the images to names I would know, so I could find them easily for my show. You can also make a folder on the USB labeled 'captures' or 'stills' and so forth and toss them all into that folder for housekeeping purposes.
When I save SWITCHER SETS I do the same thing, I rename the set to the show name.
#Carbonite