Direct port I/O under NT without a driver

I've played today with ZwSetInformationProcess and found Process UserModeIOPL information class that can be used to grant direct IO permission to a process. However, it needs that the current account has SeTcbPrivilege granted - "Work as a part of operating system". Code enables this privilege for current account, but changes are visible after next logon. One question follows - if there are no changes till relogin, why GetTokenInformation returs that this privilege is enabled? But call to ZwSetInformationProcess returns STATUS_PRIVILEGE_NOT_HELD.

ry.pl/~omega/progs/DirectIO.rar