[ic] How do I Change default payment_mode text?

[interchange-users@icdevgroup.org (..)]

I know this has been asked before but I can't find an answer, I want to
change the default [payment_mode] text from "check in the mail please
call" type of thing (as it appears on receipt.html or email receipts
etc) to something else, particularly for the mail in option.

My store accepts PayPal as the payment method and I don't know how to
add a new payment method and change everything so I'm using the mail in
format so I don't get credit card validation requests etc on the
checkout. 

Hope someone can help.

Gerry