The answer is, "it depends what you do with it." In the Advanced Rules, all that matters is the end result, when compared to the original, not the process of getting there.
*In general* Topaz Restyle is OK: basically what it mostly does is warp colors by assigning different hues to different luminance values. There may be things it does that aren't kosher but I haven't encountered them yet myself, and I use it fairly frequently.
