When Samba4 work in AD-DC mode, password policy can change with samba-tool:

Disable password expiration for the Administrator account :

samba-tool user setexpiry Administrator --noexpiry 

Show domain level password options :

samba-tool domain passwordsettings show

Disable password complexity at the domain level :

samba-tool domain passwordsettings set --complexity=off

Disable password history at the domain level :

samba-tool domain passwordsettings set --history-length=0

Disable password min-age at the domain level :

samba-tool domain passwordsettings set --min-pwd-age=0

Disable password max-age at the domain level :

samba-tool domain passwordsettings set --max-pwd-age=0

Disable minimum password length at the domain level :

samba-tool domain passwordsettings set --min-pwd-length=0