You wouldn't want to use it for a training film but I did manage to take
possession
of {9E56BE60-C50F-11CF-9A2C-00A0C90A90CE}, along with the subfolders,
and grant full permissions to System, Administrator, and myself for all
keys.
However, that said, I decided to import the original registry key status
back in because instead of "email" the revised registry entry created a
folder in SendTo named "Compressed (zipped) folder.ZFSendToTarget",
which did not appear in the Windows context menu and couldn't be opened.
Thunderbird.lnk still works, and if I rename it email.lnk (or whatever
the original name of it was) then even the cosmetics work. And MailTo
works as it should when I click an email address using FF - it may not
have been corrupted to begin with.
So thanks for your input. On the premise that life is short, however, I
think I'll take a pass on bird-dogging this one