Is there a way to change the word RECEIPT to a different text or word?
The word "RECEIPT" is coming from Merchant Facility level field called "Receipt Label" you can change that to "Any Text". But since its coming from Merchant Facility Level, it will be generated in all the Payment Forms available. In order to avoid that, if you create a separate Merchant Facility for "Any Text" could solve this requirement. Otherwise you can upload an image of "Any Text" in Letter object, which would override the word "RECEIPT".