First off, thanks for the help, everyone! I'm already impressed.
Since you've all been quite cooperative and helpful, but I could still use a little help with specifics, I figured I'd be less vague.
The changeling's inventor-personality name is "Argus" (no relation to the Argus of Jason & the Argonauts), and his inventions pretty much run in the same vein as Daedalus - labyrinths, wings, that sort of thing. Now that he has a name, it'll be a bit easier to talk about him.
Argus wants to keep "Argus" around, but since he's currently wanted by local crime lords, the local king, the representatives of a foreign army (and most every resident army), and almost every person who has misused his inventions and blamed their failures on him, he tries to be hard to find. He's currently hiding as a wine-maker, because while it's good not to be found, it's also good to have a steady income, and the personality has worked for him for a while.
Changeling Rules - They can change their body, but not their clothes, so he probably does have clothing stashes all over the place for quick getaways. If he doesn't have these stashes, then he is surely working on making them. True Sight will quickly reveal a changeling's true nature, but my players (and everyone else after him) does not have access to True Sight... yet.
Playing the apprentice running errands for the master is a brilliant idea. I had toyed with Argus being Human with a changeling apprentice, and later decided Argus was the changeling. It somehow did not occur to me that he might also be the apprentice/outside contact. This is exactly why I needed help.
On Inventions: I had also toyed with the idea of a marker on each of his inventions, and like this as an alternate way to find him (I always like to plan multiple possibilities, particularly when they make sense). But what might he have invented that I could put around the town? I'm not much of an inventor myself, so all I've been able to think of so far have been Daedalus's notable inventions (the labyrinth and artificial wings), a wind-powered automatic wine-press, and "some practical joke junk" like novelty chattering teeth and such. Any ideas here?
When I get around to running this, of course, I'll fill everyone in on how it goes.
I'm not looking for everyone to write the game for me (that would be difficult and accomplish nothing!), but I also know that if I don't start looking outside my group for inspiration, they'll start to expect everything I throw at them.