Here are some ideas I thought of that current TMs/HMs can play in the Overworld to have more use:
Cut: Be able to cut small trees, vines, grass, Spider webs, ropes or any cut-able obstacles.
Defog: Removes Fog or any fog like things in the air. So basically it should be kept the same but made a TM
Dig: Escape from dungeons and be able to dig up shiny spots on the ground which have items.
Dive: Should be kept the same as in R/S/E
Flash: Should be kept the same
Fly: Should be able to returned to any previously visited Pokemon center area. We should be able to use Fly on lightened areas in the over world and explore "Sky routes" similar to Underwater(I so want my castle in the sky). Also, cracks in the ceilings which will appear as lightened areas in dungeons to get to a higher level when there are no stairs or whatever to get to the next floor that could be part of the puzzle.
Hail/Rain Dance/Sandstorm/Sunny Day: Change the the route's current weather to that. It stops and goes back to normal once you enter a building or leave the route. it can be used to find certain Pokemon.
Rock Climb: Should be kept the same
Rock Smash: Break rocks and cracks in walls or the floor.
Strength: Be able to move boulders and heavy objects, not just boulders.
Surf: Should be kept the same
Teleport: Be able to return to the previous spots were the "teleporter" is. The "teleporter" would be like an area that does not have a Pokemon center in which we can warp to so they would look similar to the warp gate in Digimon World DS, if anyone's ever played that game. Like say there is a "teleporter" on Route 35 we can use Teleport to teleport back there any time we want. They could even be in Dungeons. So this could be either a TM or become an HM.
Waterfall: Should be kept the same but made a TM
Whirlpool: Should be kept the same but made a TM