I would recommend to the OP to reread your fare rules carefully. HOU/IAH has one of those same-city arrangements that unless your fare disallows it, you are permitted to stand by to/from the other city airport (this applies to EWR/JFK/LGA, DCA/IAD, DFW/DAL as well). Because of the aircraft type to IAH vs. HOU, it is far easier to stand by DFW-IAH instead of DFW-HOU. Keep in mind this does not apply to coterminals (LAX/BUR/ONT/SNA), those cost $25 to switch over.

My last experience with this was DFW-IAH on an L26D fare. The trip got cut short, and I had to fly back early, but L was not available from IAH, but was available from HOU. So I switched the fare to HOU on the free change for L26D fares, and stood by from IAH, got my boarding pass at check-in because the plane was so empty.

Additional thought: Because you were rerouted via IAH because of weather, you may ask to be confirmed to IAH for that reason w/o a change fee.