Hi Melanie
Artem has already mentioned the PRGN_CUST configuration which is used for PSS, Generate Password in SU01 and SU10
Your requirement sounds a little concerning to want to give users initial passwords to the back-end that is the same. Aren't you at risk of a security violation or risk?
There's a reason why SAP never developed the functionality to mass reset users to have the same password.
Also, if front end has a 12 password limit it sounds like it might have less password strength/protection which is also a risk.
Can the software configuration be done as SSO instead so you don't need to issue SAP passwords? Instead, the back end password is deactivated?
Regards
Colleen