How often does a user on kRO have to change his PIN code? - You don't have to change it ever if you don't want.
The PIN code system checks for the KSSN on AEGIS, I would say we leave that out or do a birthday check instead. Which would mess up the client translation, because that one says "You cant use your KSSN". - Leaving it out for now is fine, I guess. Other opinions?
How can a user delete his PIN? - You cannot delete your PIN, you MUST use it when enabled.
When is the button for the pincode system displayed in char select? Send state 7 to find it there. - Right after getting to char select
Has anybody got an UI translation for that system? - This are the translations, I can come up with all the buttons - if needed.
How often can a user enter his PIN code wrong and what happens then? - 3x, nothing really, you get kicked back to the login screen and have to log back in to char select.