Modifications to the invoicing and payment modules

Hello everyone,

I need to make some modifications to the invoicing and payment modules in Dolibarr 18.0.1. However, I prefer not to touch the source code directly. Instead, I would like to create a custom module that is similar to the ones already present in the source code so that I can modify it as I wish without worrying about losing my changes during an update.

Does anyone have advice on how to clone these modules so that I can customize them safely?

Thank you in advance for your help!

Question is too large to get an answer.
It depends on which feature you plan to clone, to do what, on which screen.
You may take a look at the wiki to the dolibarr developer doc to know all things possible to do with a module…

My goal is to be notified by email when I need to edit an invoice for a client, based on their billing cycle. At the same time, with the notification, I want to provide détails about their subscriptions.

I thought about adding a section in the third-party interface as well as in the invoice interface where I can put all the information I need.

I would like to avoid adding code outside the custom folder and I am already using private notes for another purpose.