Good idea, thanks for the suggestion; I've brought this to our Lead Developer's attention, so we'll add it to the wishlist. :^) Unfortunately, we don't have a way to add that exact modification yourself, and because ours is a centrally-managed solution shared in common among all sellers using our system, there is no way we or you could add that just for your cart, so it would have to wait until we could work it into to the master cart script that everyone uses.
That said, you can customize some existing text in the cart, if you wish. I'd recommend adding the following lines to your View Cart code on every page, just before the "// -->" line in the standard code you obtained from Seller Admin:
function EJEJC_config() {
EJEJC_POSTCALL=true;
}
function EJEJC_shown() {
jQuery("#state2").attr("innerHTML",
"Required to calculate shipping<br>Update Cart after entering");
}