Welcome, @DavidBarnes.
Yep, it’s possible to modify a HubSpot form’s embed code and add a GA callback within the onFormSubmit event.
Here are some related articles:
- Adding custom Google Analytics code to forms in HubSpot
- Trigger Google Analytics Event with Form Submission
You’ll have to embed the form within a custom HTML module on your template or page rather than the default Form module to modify the embed code.