I can just drop my knowledge about "henka waza" and "Kanren waza" terms how they are used in Iwama Aikido.
As a student of Saito Morihiro Sensei and of my father, that's what I can say about how these terms are used in Takemusu Aikido.
Henka Waza (as usually intended by Saito Morihiro Sensei when teaching seminars) means basically any variation from a basic form.
So for instance Kosa dori nikyo, when performed directly (chokusetsu) by fixing your opponent's hand on your wrist and applying immediately the key. This is intended as henka.
Usually "henka waza" is used to define a variation that Tori chooses to apply.
When Tori NEEDS to change his technique, so when he NEEDS to apply a variation in traditional Aikido we call it "oyo waza" (application of technique): that's actually the same way this term is used in other martial arts as well.
Example: When performing Nikkyo your opponents extends his arm you need to apply the key in a different way from the basic: but in this case the need to change comes from your opponent (thus in henka waza it depends on a tori's choice, usually)
Kanren waza concerns something completely different, which can't be confused with the concepts above: it means "combined techniques". That is actually the way Renraku waza were called in Ibaraki prefecture current dialect, as far as I know. And that's the term Morihiro Saito Sensei used to use to define combined techniques.
In this case it doesn't make a difference if tori combines different techniques because of uke's reaction (which forbids him to complete the initial technique) or because he chooses: in both situations they can be called "kanren" or "Renraku".
Sometimes Saito Morihiro Sensei used also "Kaeshi no kanren" to express a situation when tori starts a technique, uke reacts (with a kaeshi waza or by any other way), afterwards tori reacts to his reaction.
Hope my post was not too confused so far!