[GNC] need to teak the default invoice script - new user

[peter]

Hello all,

I am new to GNUcash - spent many hours getting to grips with the new 
system (came from Quick Books) and finally got my small business 
accounts set up and working reasonably well.

However, I operate two trading names of the same business and need to be 
able to invoice the two types of clients with different invoice 
layouts/content.

Could someone please tell me the following:-

     Where is the default invoicing script stored, so that I can tweak 
the code to my needs for client type 1 ?

     How can I add a print menu / toolbar  item, that points to an 
alternative "default" invoice script, that I can use for client type 2 ?

I have spent many hours playing with the built in facility to change 
invoice layout, but it doesn't quite meet my needs.

I am using GNUcash 4.8 running on Ubuntu 22.04

Any help to point me in the right direction would be greatly appreciated.

Kind regards

-- 
Peter Jubb