Yes, but here's the thing.
If you look at the larger diameter of the battery holder, the end which comes in contact with the head of the light, and now look at the outside wall diameter of that section. It is not a perfectly round diameter. It has a larger rounded 'bump' if you will sticking outward from that radius. This 'bump' or 'key' allows the holder to index into the body in only one way. It can not be rotated 180 degrees so as to mismatch with the switches at the bottom end of the holder/body point
The body of the light has a matching key cut into the inside diameter of the wall. If I try to reverse the holder by 180 degrees to slide it into the body, it will only allow the holder to drop in as far as the hight of the batteries. The larger round head of the holder will be stopped by the indexing key, hitting the lip of the threaded section of the body thus stopping it from going all the way down into the body. Even if that was not noticed, and it can not be on my TK35, if you tried to screw the head onto the body it will not even come close to the threads engaging. There will be a gap between the light body thread section and the head threads by more than half an inch due to the large diameter of the holder being in the way.
Simply put...it can not happen.
What I am curious about here, is did Fenix make a change at one point due to an over sight which allowed an earlier version of the TK35 to have it's pack inserted wrong by 180 degrees. This is what I would like to find out.
And actually, as I am typing this, I just looked at the "FenixTactical.com" web site and the photos of the battery holder clearly show the key, or bump, that I am talking about.
Have a look at the picture in the photo gallery for the TK35 there.