Dear Geoff,
from this explenation: "some non-ascii characters are now replace by '-' before writing URLs to tvh's config", ...the script will only replace those non-ascii characters with dashes.
As far as I know, there are no such non-ascii characters in "Channel 5 HD", so it should only take out spaces, change to lower case and symlink "Channel 5 HD.png" to "channel5hd.png"???
Maybe you need to find another icon set or I am missunderstanding your question.
I used icons from dvbviewer, because I have a license from my old windows days for this program (you need this to download the icons) an it worked well.
I am sorry, this won't help you much!