Hey Larson Lawn Care,
There are no limitations during the trial period, so yes, you can sync with QuickBooks. If you set up the sync however, it will indeed synchronize your customer information. If you make changes to customer data you can expect those changes to push back into QuickBooks as they should.
If you're concerned about not actually impacting your QuickBooks file then I suggest you not hook up the synchronization. The other option is to create a new test QuickBooks file to synchronize with. I should also mention that many of our customers are actually finding that they can ditch QuickBooks entirely, since we do Invoicing & Billing, Payment Tracking, Expense Management and Reporting quite nicely right inside Jobber. Might be an opportunity to simplify your work flow.
Sam @ Jobber