Mystify,

I like what you are going with here. I just got my PDF for Ultimate Magic from Paizo. They have a substitution class that is might fight some what into what you are trying to do with your class. When it finally hits some of the free sites out there take a look at wha they do with the Summoner class with the Synthesist. It is not a true shapechanger. You are more of a merge into the Eilodon that you summon than you are your own Eilodon.

Now on to your class. The problem with a shapechanging character is that if they are always able to do all the time there will not be as much challenge, or much choice, they can just adapt to about any situation and over come it with out any type of fore thought. It would become, Oh, there is a fire pit, okay time to switch out Gills 2.0 for fire resist since we don't have to swim any more. Then so, on and so forth as each challenge is presented. Now, doing that every once in a while is COOL, doing that for every challenge is boring.

How about this, about an hour ritual each more that this changer has to perform so they can be ready themselves to change certain parts of their bodies. Say Either a base 1/4 or 1/2 of their total pool can be changed on the fly to about anything they want... Or maybe they have certain portions of themselves that are always in flux. Where they have can change one evolution out for another or multiple if they are different point costs.

Say I have Flight a 2 point evolution going so at a set level I would allowed to change that out for another 2pt evolution or two 1pt evoltion, so I could get extra claws and then pounce.

Just allow the character to change each morning after an hour of meditation with forms they would want to change, and what they can change them to. So instead of whole sale change, they would only be able to change them into set things?

Just a couple ideas.

Oh yah, I think you will like, the Synthesist... I think they decided they wanted to knock the Summoner up a tier... Or two...