If your gun isn't a stainless model, then any changes need to be dealt with by a gunsmith.
But that's getting a bit ahead of yourself. First, make sure that the gun is 100% reliable. There's no point in spending money to modify it to the perfect carry gun if not reliable enough to be a carry gun in the first place.
My PPK is stainless, and I've made a few changes to it. I took the sharp edges off the bottom of the slide rails--there's no need for the edges to be razor sharp. Be sure to deal with the bottoms of the slide serrations--they're like sawteeth. I also rounded the back corners of the slide, the hammer burr, the corners on the rear sight and the "beavertail" to make it more comfortable to carry.
If done properly, these modifications are barely noticeable. It doesn't take a lot of metal removal to make a big difference. But, if your gun is blued, it will need to be refinished when you're done.