Change from "inclusive" to "exclusive" tax and updating pricing for all applicable active services

I am looking into the feasibility of switching from "inclusive" pricing to "exclusive". I have opened a ticket with WHMCS support to see if there was an easy way to update the pricing for all the active services (excluding the services/clients that are not taxable eg, outside the EU) and they said the only way to do this would be to manually correct the price for each active service via WHMCS, not realistic if you have thousands of active services in the system. I was hoping there would be a table in the database that we can just run a query on to update the price minus the tax but WHMCS support suggest there is no single table that this could be done on and therefore it's not possible. Surely there has to be a simpler way ;) Has anyone successfully made this type of change within WHMCS? Thanks in advance.