Hi ChrisV2,
the MOD is still in RC here, on phpbb.com, because I tried to submit it a couple of time and it was denied with, in my personal opinion, not so strong reasons, like:
move_attachments_in_subfolders.php should be called move_attachments_to_subfolders.php or something similar.
and similar...
I don't have so much time to spend in fixing all these kind of negligibles details, so I decided to quit and leave it as RC.
On the contrary, the italian phpbb support site has approved the MOD, and as far as I know, a lot of users used it with success, and is more than 1 year that I myself use it on my board, so I think it's quite stable.
You don't have to change anything on move_attachments_in_subfolder.php.