Yes, as long as your order isn't being packed or is out for delivery.
To change the flavours of food your pet receives:
Go to the Subscription page in your account
On the ‘What’s in your box’ section, select the button labelled ‘Change flavours’
A pop-up screen will appear detailing your current food selection
Reduce or remove the flavours you don’t want
Increase or add flavours you do
Once done, click the button labelled ‘Save Changes’