Create ARTMAS idoc triggered by a change pointer (filters, add data)

My requirement is to create an ARTMAS(ARTMAS02) outbound idoc triggered by a change pointer. I have just made the configuration of that point but my doubts are now in these two things:

- Where and how I could check segment field values?  Is there any badi or user-exit for that? I pretend to avoid the creation of the idoc if the fields don't pass the validations.

- Where I could add or change the values of some segment fields?

Thanks for your time.

Best Regards.