Since May 2015 (IIRC) there have been no official restrictions on accessing any terminal at an airport in the USA as long as you have a same day BP for a flight departing that airport.
Moreover, the terminals are becoming more an more connected airside. e.g. At LAX it is possible to travel airside between T2 and T8 (walk between TBIT and T8, Bus between TBIT and T3/T2).