Hi rener,

Currently there isn't a way to create Client Groups or sort clients into a custom category. However, what you can do is to change the Display name as within the Edit client section to a name of your choice, for example adding brackets after the name to identify the client as registered for GST or not.

I would recommend recording this as feedback from within QuickBooks Online Accountant, so our Product Teams are aware of this so they may consider adding this to QuickBooks in the future. To enter your feedback, select the Gear Icon on the top-right, and then select Feedback.

Bonny