I've received my T440s yesterday. It came as replacement for a failed T420s that according to Lenovo Europe, was beyond repair.
Since they sent an extra 4GB RAM to match the configuration of the replaced unit, and I had to fit my SSD, the unit
had to be opened.
As all others have pointed out, that is not fun. I understand that Lenovo eliminated independent access to internal devices because of the anti-tamper feature, however that is a major trouble for DIY users and repair shops. Lenovo could still have made a bottom cover with openings for users not requiring anti-tamper.
Here is how you can open the bottom cover without damage:
If possible at all, use a plastic cellphone opener tool:

If you use a metal flat screwdriver, you
will almost certainly cause some marring and/or break a latch. I did not had the plastic tool and broke "only" two latches with minor marring, while working with very limited use of my right hand because of an accident.
This is the technique I found to be most effective.
Start with the two latches under the battery. Pry just enough so you can see latch opened, and fit in a piece of paperboard to keep it. Move to the side latches.
The key concept is to
not try to locate exactly and hard push in the latch, especially when using a metal screwdriver. Just push and pry gently in the area where the latch is, the shop manual is accurate enough for locating them. As soon there is enough space, fit a piece of cardboard and move to the next latch. Do not insist against any single latch, move to the next and you will find that eventually all will give in.
Then, even with all the latches crack opened, the cover will not come out yet, you will have to lift it gently on all sides to remove it.
The unit booted with the T420s SDD and once loaded WiFi drivers drivers from USB I was good to go with system update. Certainly many things are different from older TPs and something will not ever be as before. However I kind of like it and I'm already productive with it.
[Added 4/17]
I've got an FHD display today, the AU unit. It came very cheap on Aliexpress, and shipped quick and cheap.
Again the manual is not clear about this procedure. This is how I recommend to do it.
Use a credit card with s sharpened edge to lift the light plastic frame only where the four screws are, that is on the log side about two cm from the corner. Remove the screws Leave a piece of paper of paper in between cover frame and bezel,, because it tends to stick back.
Using the same tool push again one the edge of the screen, but this time you will have to go under the actual plastic bezel. As you lift a little, the latches will give in. These are small and very well made, as you list the the bezel all around, you will be able to remove it easily.
Flip the display and remove the sticker that holds the cable connector in place. You will have to start on the long side and work slowly, as a strong adhesive is used there. When the plastic sticker is lifted, you can pull out the cable and replace the display. The sticker/holder should have enough glue left, or use some new one.
To fit the bezel, start with the long side by the hinges. Keep it 45 degrees and slide it back and down. If you don't do this the latches on that side will not go in place. You will have to close the display to check on that.
If these are OK, place the screws back in, press the bezel to snap in all around, and your new display is ready to go!