At the end, the best (i.e. safest) way to upgrade Kobo Aura HD internal memory to 64GB is "from behind", i.e. by cutting away (using a soldering gun) a small rectangle which opens access to the microsd card, see the pictures below:
http://www.bibles.org.uk/screenshots...anced-pic1.jpg
http://www.bibles.org.uk/screenshots...anced-pic2.jpg
Also, I found a position at the top edge (about the middle thereof) where a slight pressure re-enables the entire screen's touch sensitivity (i.e. probably realigns those shiny plastic bits). Sadly, while experimenting to find this area I accidentally pushed at the top of the screen too hard and damaged the top part (about 1cm worth), so the reader is now unusable. But the technology of the upgrade is now proven, so I am going to collect my newly ordered Kobo AuraHD in two hours and perform the upgrade on it in this manner.
Let me emphasize (for those who didn't read my previous posts) that the loss of IR functionality occurred because of the removal of the front plastic stuff which INEVITABLY disturbs the IR guiding bezels. So, by cutting a "window" in the back cover one avoids the need to remove the front bit altogether --- so it should be perfectly safe. One just has to be careful when holding the soldering gun not to touch the motherboard and solder/unsolder some things on it as well
Also, I did it with some short bursts and 5-minute intervals to let the area cool down, i.e. not overheat too much as the soldering gun has 600^C temperature and I have no idea what is the "maximum safe temperature" for the device...
And the presence of the "window" in the device is irrelevant, because it is always held in the protective cover anyway. So the cover closes this hole tightly and no dust can get into it.
Unless someone tells me of some obvious FAULT with this process, I'll do this on a newly bought Aura HD as well, because it didn't seem to make any damage to the old Aura HD.