By government policy and in practice, a valid boarding pass for a flight departing from any terminal at ORD on the particular date shown on the boarding pass is acceptable to go through TSA security at whichever ORD terminals the passenger named on the boarding pass chooses to use on the date indicated on the boarding pass.
And the boarding pass can be used repeatedly on the same day to clear ORD security screening checkpoints repeatedly without any problem from the TSA as long as the checkpoint is open for any passenger screening.
If the TSA ID checkers tell someone they are in the wrong terminal, I would just say there is an airside shuttle bus option or mention visiting a lounge or restaurant. Personally, I haven’t had TSA ID checkers even mention my being in the “wrong” terminal at any point in the last two years since TSA ID checkers at ORD shifted to using ID scans to electronically pull up passenger records instead of being as reliant upon scanning boarding passes handed over to them.
Some airlines or the airport have contractors that control access to the premium passenger security screening lines at ORD. If avoiding those “first/business/premium passenger” type lines, then there is even less chance of anyone saying anything about being in the “wrong terminal”.
