Adding stock to a pre existing business

We  have been using the Quickbooks Online software for numerous years now but have never really fully utilized the product or explored its features as we mainly use it for invoicing, expenses and keeping track of payments.

We have recently decided that it would be beneficial to implement an inventory system through QB Onliine, is it possible to start this halfway through our financial year without it effecting our sales / expenses figure if we input pre excisting stock?

Thanks.