The .32 S&W Long typically loads a 98g bullet at 750-780 fps. The .32 H&R Magnum loads a 95gr bullet to 1020 fps and the 85gr to 1100 fps.
SAAMI lists the .32 Long pressures at 17,000 psi, but unfortunately the .32 H&R Magnum is 21,000 cup (copper units/pressure), which is not comparable.
But as to your original question, I wouldn't have a problem with doing that. As long as you limit the use of the .32 H&R Mag and closely inspect the gun for throat erosion or cracking.
Rather than change the gun, if you reload, I would carefully work up some "hotter" .32 S&W Long loads. Watch for signs of excess pressure and back off if you encounter them. This way, you don't have to spend the money on modifying the gun, just the ammo/loads. The .32 Long cartridge has room to play around as long as you carefully work up your loads.
With that said...
If you're thinking of a defensive gun, you might want to look at the S&W 632CC or the Ruger SP-101 chambered for .327 Federal Magnum. This new round is an elongated .32 H&R and a true magnum that pushes a 100gr bullet up to 1400 fps (from a 3-inch!) and operates around 40,000 psi. Muzzle energy is similar to the .40S&W.
If those are too pricey, you can probably still find a .32 H&R Ruger SP-101 in the distributor network or a S&W 431PD/432PD. I have the 432PD and it's sweet. But I'd rather have the .327 Fed Mag for the power. And the fact it will shoot the .32 H&R. .32 Long and .32 S&W makes it pretty cool.