At no time are you allowed to be part of another GTA 4 clan while you are a member of Liberty City Departments(LCD).
You must register with your PSN name.
No use of RPG's are permitted EVER by any department.
No use of Super cars such as Banshee, Super GT, etc. by any department.
Civilians are NOT permitted to use helicopters EVER.
Only SWAT, LCAD and a select few LCPD and LCED are allowed to use helicopters.
SWAT can use any and all weapons/vehicles except for the RPG and supercars.
Only SWAT can use APC.
In order to become part of a Department you must submit an application to the department of your choice once you have registered with the website.
There will also be department specific rules & regulations on their various pages.