The way I have gone about it is by going to spawners/startup spawners/GDI spawner +modify setings/presets/pick presets then add and remove the ones i want form the soldier presets list.
what happens is that in the LE it does change the character of the spawner, ex. it was a minigunner now it looks like an enginer
however when i test it in multiplayer Lan I still spawn as a minigunner. is there a global setting or something I am doing wrong?