There are a couple options:
OPTION 1: Is the store going to be charging tax on the items? If not, then the easiest thing to do might be to just set the "cart_show_totals" parameter of the uShopOrderButton applet to "NO". This will cause only the "Subtotal" to be displayed on the final order form. And then you can just add HTML/Text to the order form saying that "Applicable shipping changes will be added."
OPTION 2: Or as another option, perhaps you can just change the "Shipping & Handling" label on the order form to something else. This can be done via the "cart_label_shipping_and_handling" label on the uShopInitialize applet. (just put that applet on the same page as your uShopOrderButton applet).
OPTION 3: If you just want to put the word "*Note" in the Shipping & Handling value cell (instead of displaying the $0.00), here's how to modify the script:
STEP 1: Make a backup of your ushop-lib.pl script... just in case.
STEP 2: Open your ushop-lib.pl script with any text editor such as WordPad.
STEP 3: Do a search on the following line:
... This will get you to the start of the subroutine that outputs the shopping cart HTML on the order forms.
STEP 4: In that subroutine, you will find TWO instances of this line:
$formatted_output = sprintf("%s %.2f",$currency_symbol,$totals_shipping_and_handling);
Try changing that line to something like this:
$formatted_output = "*Note";
STEP 5: Save the script... as TEXT if your editor asks... and try it out!
NOTE: You may want to make the same changes to the "sub get_cart_text" subroutine which handles generating the TEXT output for the email receipt.