With a rod-like stone, diamond rod, ceramic, or file of the correct diameter, scalloped blades are relatively easy, if tedious, to deal with. Serrations of other than circular profile can make it tough to find media. If you are going to sharpen freehand, get a junker to practice on before tackling a good blade. I never found one to buy, and did not make my own, but a jig to hold the rod and allow handling more like dressing a straight blade on a large flat stone would ease the tedium and speed the process. I was almost grateful when a thief got my last serrated knife and provided the excuse to replace it with a straight blade.