How can I add line to the record system note or create system note?

What do you mean? They're read-only as far as a user/script is concerned. You add to them by modifying records. What is your actual requirement?

@PNJ when someone modify the record I want to add extra customized line to the system Note

I guess one way of doing it would be to use another field on the record that you modify with your customised message in a beforeSubmit() UE

Well that'll be just old and new value

Like I said, you can't (for good reason). It's an audit log.

you could create your own audit log custom record.

@stalbert how that will be added to the record I want

You'd need to have a user event script or something which would add an instance of the custom record each time a user edits the target record.

@PNJ @battk I've added a new hidden column field and in my script I load the record and set the value for that field, but there is no sign in system note, am I doing something wrong?

ive found that line item history tends to work out better for recording changes in value

@battk I've set the default value, but still the same.

well, that should get you a system note on new transactions