How to disassemble / take apart Fujifilm X-T1 and how to disable ISO Dial lock switch.
It is relatively easy to take apart FujiFilm X-T1. You only need one type of screwdriver, although the screws themselves are different. So as usual, make sure to have several small containers and a piece of paper to write down/draw where a particular screw came from. It took me less than half an hour. And I had no idea what I was doing. Took longer to document the process :)
The way the camera opens is, the top part comes loose and the back slides out, separating from the front. WARNING: DO NOT remove the top first. Just unscrew it and notice that it is loose and leave it be. The reason is that it has several short ribbon (film) cables, and if you lift it up first, you're likely to disconnect or mis-align them, or worse!
So first remove all the screws that I will mention below in diagrams, then slide the back side out, and the then the top will easily lean back. The back side is preventing it from leaning back. Here in this photo you can see that I tried it at first without removing the backside:

As you're removing the back side make sure to support the top so that it doesn't fall, pulling on the cables. Back side also has ribbon cables but it's much more easy to handle, they're only attached towards the bottom (see image below).
So if you do everything right, no need to unplug any of the cables. If you've ever dealt with ribbon cables you know why I'm stressing this part so much. They and the ports they go into are very fragile and difficult to handle. Tweezers can scratch them and even cut the connection. (Here they're not that big of a deal as in Fuji lenses I opened previously, but still why bother if you don't have to right?)
So, lets do it step by step.
1) Bottom: there are 8 screws - unscrew all
2) Front: only 1 (small) screw on the right side, peal off the rubber covering.
Left/Right is when facing the camera.
3) Left: 2 above, 2 below (all behind the rubber)
4) Right: 2 above (behind the rubber) and one behind the USB door
5) Back side: Lift up the viewfinder rubber guard to reveal 2 screws, and flip up the LCD to reveal two screws there:
The lower part behind the LCD has 4 more screws. Those ones only hold the LCD in place. Don't remove them.
6) Once these screws are removed the camera can come apart. Again, don't pull on the top part. Slide the back side out as in this diagram:
It comes apart this way, so the middle sides belong to the front part. That's why in the previous pic I'm pushing the top edge out with my index fingers and bottom with my thumbs.
7) And it opens up like this
8) Now with the back cover down, the top part can be leaned backwards easily:
9) And you have access to the ISO dial mechanism. Just unscrew that middle screw and follow the diagram to remove the evil silver ring. It actually snaps on/out. So if you ever wanted to put it back, it's a possibility.
10) And here's how it looks like inside.
Before doing this, I was wondering if there's a spring inside etc, and that afterwards there would be a hole I would need to seal... but none of that!
Once you take out the ring and close up the camera, the button is still in place and presses down like before, except it has ZERO effect now! The ISO dial still clicks as you rotate it, same as before. It's like the magic fairy came and took only this silly ISO dial lock "feature" away without any side effects, with an exception of course, that you actually have to do it all yourself ;)