To change your delivery address for just the one box (for a holiday in the UK, for example) start by logging into your online account with your email address and Butternut password.
Click 'Deliveries' in the menu at the top of your dashboard, and scroll down to find the delivery that you need to change. Click 'Show details', and then 'Edit address'. Add the new address and click 'Change address', and then you're all set.
Only this box will come to this address - all the rest will go to the default address on your account which you can find in your 'Personal Details'.