Adding Custom Field to Quotes after selecting Account

Hi all,

im quite new in developing in SuteCRM and i have -maybe- a simple question.

I have a custom field in accounts called “account_discount”. I holds the standard discount for this account in it. For example “10%”.
After creating a new Quote and selecting the Account i want to add this discount to the field Discount at Quotes.

Is this prossible? I found the logic_hook after_relationsship_add. Is this the right way to do that?