"Soloid" said ...Realtime texture painting is not a feature fitting for a game engine, so it's not in SFM either. If you want to paint directly on a model, there is no way to do that without decompiling the model and getting it into Zbrush or Photoshop's 3d painting mode. But if what you're doing is restarting SFM to see your material changes, you can see your newly saved texture easier without having to reload SFM. Use the Model viewer included in SFM and load up a model. Pressing F5 will instantly reload the model and its textures. In SFM you can also enter mat_reloadallmaterials to reload all textures without having to restart the program.
Is there an easy way to see in real time your model when texturing it? (Currently I have to reload SFM to see the changes).