I'm affraid that you have violated the isolation of the meter. I'm not sure how this unit is build but bare usb ground connector doesn't look safe in this solution.
The shield of the USB connector is not connected. For my application, test and measurement on battery powered material handling equipment (i.e. forklifts); I am not concerned about isolation. Of course anyone who would perform this modification should understand the inherent risks if measurements on live mains circuits were going to be performed. In my case I do not do service work on mains connected equipment, the very minimal risk is far outweighed by the benefits gained.
It's a cool idea.
Just make sure you're not making measurements while the meter is connected to your PC's usb.
Make sure the charger is fully isolated.
Thank You, the point of this modification was to not have to connect a charger to the meter during extended use.