Great help, thanks !
As others pointed out, steps 10-11 and 13-16 are not really necessary.
Took me less than half hour, and by taking my time and being extra cautious.
To get the HDD (or SSD now) back in place, I used a small adhesive tape to keep the part with the side torx screw up and aim for the corresponding holes while pushing it back. And removed it afterwaeds.
I saw there is room for a second one and and a second SATA, I'll try to add onther with the proper iFixit guide :)

Just finished in a little more than 1 hour (no rush, just to give a hint). I have two kits with two iOpener, it speeds up things a bit. And it’s my second time opening this iPad, after a battery replacement two years ago.

You shoud add hints a to remove protective adhesives before assembling it back, I almost forgot to remove the inside one of the glass :). And also one should be careful when removing the red tape from the glass (that marks the digitizer) : I peeled it a little too fast and some residue stayed, fortunately it’s not visible once finished.

Oh in fact it is a real step in the english tutorial, not in the french translation.

[Pour les francophones, vérifier la version anglaise qui donne plus de détails par endroits :) ]

Nevermind, a lot of help here again, thanks everyone :)

Just did it too ! Original battery went down to 53% health, getting really low. Took me forever to remove the battery at the end, many heating and trying, but the reverse steps were a lot faster. thanks iFixit and guide writers.

As with my iPhone teardown, always some glue getting around (screen) thats quite hard to clean, and I didn’t clean enough the back of the glass before putting back the adhesive strips, endin with half a mm more in a corner.

Success too ! Finally took the time, the guide is neat, but it got me sweating a couple times :) I just did the battery adhesive wrong, replaced it with two-sided tape, hope this works with time. The screen adhesive is kinda annoying too, but it was included with the parts, so no complain there. Many thanks to iFixit as always, I can now keep my 6S a lot longer !