Dear Khairy,
You can do its via config only. GO to account group setting - select your account group for which you are going to create your customer master i.e. BP. In field selection - you will find the 3 option as general data , company code data & sales area data. - select company code data (as required) - double click and you will find 4 option Required, optional , display & suppress - here you can select the option required by you.
Thanks.
SS