Yes, while creating a new purchase order or after opening an already existing one in the Web Portal, you can add individual Terms & Conditions which will only show up on that Purchase / Expense.
In the Web Portal, go to Accounts > New Purchase (if creating a new Purchase Order).
or go to Accounts > Purchases > select the edit pen for the Purchase.
Inside the Purchase order window, you can scroll down to the Terms section. Enter the Terms & Conditions details here, and then select Save at the bottom of the page.