If a bill has a partial HST, how do I change it without changing the total amount?

Hello Glamorlk,

Welcome to the QuickBooks Community. It's important you get the help you need so you can continue to manage your work with peace of mind. Don't worry, I'll be happy to steer you along the right path so you can continue to do the things you enjoy. 

It's important to note that changing the HST amount on a bill will change the total amount. Are you working with a custom tax code that requires a specific rate? If so, have you looked into setting up and using a custom tax code? Feel free to share any other valuable information that can help me get a better visual of what you're looking to accomplish. You're more than welcome to send screenshots as long you cover any personal information that may appear on the screenshot. 

I look forward to hearing back from you in the comments below.

If your bill has partial HST charged on it you can edit/overwrite the HST amount that is calculated. 

Click in the HST box/field (below the Subtotal) and enter the actual HST charged.  When you SAVE this entry the HST will be saved with the amount you entered.  NOTE: if you make any edits to the entry it is possible that QBO will recalculate the HST and it will be out of balance with your original entry...