To make changes in the description field for each line item in a Project in the Project click on Descriptions tab. You'll see the option to modify the Work Order, Quote or Invoice there. Changes here will only affect that invoice/Work Order/Quote.

 

To make company wide preference changes:  In Preferences module-> Forms you can set up what information you want to appear on your reports as a default.

 

You may also create Invoices unique to each customer in the customer module. This will over-ride your company settings in Preferences when this customer is selected in a Project.

In Customers -> Invoice Description Line Format