If you are going to remove 1/2 the insulation, you might as well remove it all. With 1/2 the door unprotected, insulating the other 1/2 is pointless. The only way that would make any sense is to remove half the thickness from every panel, and leave none uncovered. I find it very difficult to believe that the extra weight added by the styrofoam is enough to make any difference to the garage door opener. When the door springs are properly adjusted to the door WITHOUT any styrofoam insulation, you should be able to disconnect it from the mechanical opener, and open and close the door with one hand. After that the garage door opener should be able to open and close it without even straining. And adding styrofoam after that won't add enough weight to upset that equation. Just trying to upgrade to a bigger motor is just asking for unnecessary problems, IMHO.