Yes it can! NethServer has two password policy options: strong or weak. None of them changes the length requirements, so if you manually change that parameter its value should be always preserved. However I cannot promise this behavior won’t change in the future!
To change that min password length:
[root@vm5 ~]# nsdc-run -- samba-tool domain passwordsettings set --min-pwd-length=3
Minimum password length changed!
All changes applied successfully!
[root@vm5 ~]# nsdc-run -- samba-tool domain passwordsettings show
Password informations for domain 'DC=ad,DC=dpnet,DC=nethesis,DC=it'
Password complexity: on
Store plaintext passwords: off
Password history length: 24
Minimum password length: 3
Minimum password age (days): 0
Maximum password age (days): 0
Account lockout duration (mins): 30
Account lockout threshold (attempts): 0
Reset account lockout after (mins): 30