its x-y- and z, just make sure you have the options set to origine.
Now this is a bit tricky because you have to make sure you start with a teen mesh because you need the teen skeleton.
Best thing to do:
*Import the adult mesh with your favorite shoes
*select all and scale the mesh to 94% (0.94)
*cut off the part above the knees
*Save this file as wanted shoes

Open the teen mesh and cut of the part under the knees
Import the adult shoemesh(wanted shoes)
Do NOT import additional bones if unimesh askes
You now have both parts,
Go into side(left/right)view and select the back of the seam(the row of vertices at the back of the knee)
choose hide selection from the menu
Go back to front view and snap the verts together(the row at the front of the knee)
When done choose unhide all and go back to side view .
Select and hide the front row of vertices(front knee, the ones you just snapped together)
Go back to front(or back) view and snapp the vertices at the back of the knee together.
That should do it.
