Solution 1

I need to change all clients that are using linkpoint and change them to authorize.net but at the same time I don't want to switch the people paying with paypal to authorize.net.

• Update tblhosting set paymentmethod = 'authorize' where paymentmethod = 'linkpoint';
• Update tbldomains set paymentmethod = 'authorize' where paymentmethod = 'linkpoint'

If you also want Unpaid invoices:

• Update tblhinvoices set paymentmethod = 'authorize' where paymentmethod = 'linkpoint' and `status` = 'Unpaid'

Solution 2

Kadeo's Payment Method Updater Addon/Module – untested but should be ok

• This addon module allows you to update all the hosting accounts for an client to a new gateway. You also have the option of updating all open invoices as well. Perfect for when they call up and go "I want to pay by xyz now".

• Version 2 Now includes domains option as well and It now has a Gateway -> Gateway option.