I've discussed with someone from EVSE upgrade and concluded that at least the EVSE wasn't modified by them. They told me that the original (unmodified) Nissan EVSE does in fact work "normally" up to 240V of power supply albeit limited to 12A, but there are at least some surge parts inside not rated for 240V, so there is in fact a danger involved although not immediate (in fact, this EVSE has been used by previous owners for years).
Anyway, I obviously want to be safe, so I'll be buying a new EVSE that is certified to work with our country electricity network. Despite of what the local Nissan dealers told me, I have found different EVSE that don't cost 1000e but they are rather in the totally acceptable 350-500e range, and as they are sold by local shops I have the possibility to just go there and try them out to make sure they actually work with my car.
By the way, I have also found this interesting piece of information related to charging voltages:
https://nissannews.com/en-US/nissan/usa ... -batteries
The articles at some point says "The 2013
Nissan LEAF boasts innovative features such as 240V charging
that is nearly twice as fast as the previous model, as well as a broader range of trim levels starting with the even more affordable S grade, moving up to the SV model and graduating with the top-of-the-line SL."
Can I safely assume that this is also the case for all Leafs manufactured after