how to code the user exit userexit_number_range from mv45afzz

Hi, i need to modify the user exit userexit_number_range from mv45afzz, this is an standard include so when i try to modify i get the request for the my access code.

Can someone explain me what is the procedure to modify an user exit.

Do i need to request an access code to modify this user exit.

am i complete lost in the proces of coding user exits?

i have already check many of the message posted.

thank for advance