You can use the “Replace Body Part with Prop” method.  Its fairly quick, but you may have problems aligning the neck joint perfectly.

1. load the original Default version of the figure with the desired head & export head as .obj

2. open new scene and import this new head.obj. DON'T MOVE IT!

3. load figure with body that you want, and translate its BODY (not the head .obj) until it aligns with the head.obj that is still in the default position. (Making the Head to be replaced invisible helps to see the upper neck joint.)

4. when aligned, select Head on figure with body and, under the OBJECT pulldown menu, use: "Replace Body Part with Prop" to attach the new head object.

It's Alive!!

Transfer all your prior morphs into the new head & delete the MT's from the old head (they'll still be in the CR2 even though the old head is no longer visible.)
Sometimes I replace the eyes also, sometimes I use the old ones and just reposition them.

The neck joint may still be visible, so try Taper & Scale to tuck it in.