is there a way to change an existing customer or vender account number? for example if the company changes its name, i would like to be able to change the account number to reflect the new name.

Use Adagio toolkit, for more info see http://www.dakotasoftware.com/toolkit.html
Contact your dealer for pricing

If you need a demo on Adagio Toolkit I would be more than happy to show you. You can contact me at rayp@accacc.com if you would like demo.