I wrote an open-source command-line tool called fexcel a while ago that reads an Excel spreadsheet and then populates the comments/labels for things like registers, position registers, string registers, user alarms, I/O, etc.
You basically tell fexcel where your data is located, how the columns are laid out and a list of robot IP addresses, and it will go and do everything for you... probably in less than a second. (Probably overkill, but it works concurrently. i.e. it takes about the same time to label one robot as it does to label 20 robots)
Make sure KAREL is unlocked under Setup > Host Comm > HTTP.
fexcel [options] filename host(s)...
> ./fexcel -sheet Data -numregs A2 -posregs D2 -dins IO:A2 spreadsheet.xlsx 127.0.0.101 127.0.0.102
You can read more about it here or at the project's GitHub repository. Download the latest release here.