OK, I'm sure this isn't the preferred method, but I was able to:

1. download the script file to my Windows PC
2. use my USB cable to copy it to the RS-MMC card on my 770
3. [install "becomeroot" then] vm the file from /media/mmc1 to /usr/bin
4. do the chmod a+x thing...

...and everything worked perfectly, just as advertised!

I then created a folder on my RS-MMC card called "youtubevids" and changed the script line for "default save dir for youtube" to:

my $defdir = "/media/mmc1/youtubevids";

and that allows me to download vids directly to the RS-MMC card. (I had to install "nano" for editing the script because the vi editor was scaring me.)

Creating the YouTube video bookmarks in their own bookmark folder works fine. The script finds them without any difficulty.

Keeping the Opera bookmarks cleaned up (i.e., deleted after use) is going to be the most inconvenient part of the ongoing procedure.

Later I'll look at running the script from a shortcut.

(Now if I can just find the forum thread that explains why MPlayer crashes and reboots my 770 unless I close all other apps and disconnect Wi-fi before running MPlayer.)

Thanks again!