How to change BC in transient analysis
 

I am trying to run a transient case in which I need to change the BC from inlet to wall at various times. Earlier Mr. Lee asked the same question and Mr Zhang mentioned that a subroutine can be used. Can anybody tell me which subroutine(name of the subroutine file) to use and if they can give some sample coding that would be really helpful.

Thanx in advance.