1) Place soldier controllable by you. Into your init line write:
this addEventHandler ["HandleDamage",{if (_this select 1=="") then {damage (_this select 0)+((_this select 2)/10000)}}];
2) Place enemy soldier(s) in front of you and play mission
3) Watch how even, when damage is decreased by 10000x, you still get killed on few hits.
4) Then set yourself as one of the enemy soldiers and make that soldier you had controlled before to be controlled by AI. You will see that It works pretty well on him. However if you would switch to him by "playable" feature, and then switched back to your guy, his invulnerability will be gone.