The WR CDI is easily distinguished from a YZF CDI by the fact that the YZF units have no attached wire harness. The harness connector plugs directly into the box. The WR ignition does have a harness, and there is a gray wire.
On a WR450, cutting the gray wire is supposed to alter the timing map
to be similar to the YZ; snappier and more responsive. The wire that is sky blue on the CDI side of the connector in the '03-'05 models connects to a sky blue/white wire on the harness side, and still passes through the neutral switch, but the circuit is different. Some people cut this because it makes the bike start a second or two more quickly under racing conditions.
The '03-'05 YZ450 was a 4 speed. It can be converted by swapping in the entire '03-'06 WR 5 speed, but that doesn't happen very often because it's rather expensive, as you might imagine. Another tell tale is that the WR neutral switch below the front sprocket will have two wires connecting to it rather than one as does the YZF.