Wow, Chris. What an interesting thread
I think the information in the entry is accurate but maybe not quite complete.
In my understanding henka waza represents all the gray area between the basic techniques. It could mean changing to another distinct and reconizable technique, but it can also mean any small variation that is required to make the technique work under the circumstances.
henka: change, variation, alteration
I think I recall hearing Saito say at a seminar that less than 1/3 of techniques will be the standard form; the rest will be henka.
That was probably somewhat of an arbitrary statement. In my experience 95% of techniques are henka.