The risk of a Kobo device spontaneously bricking itself is a lot less than you think. And that includes if you count the number of requests for images made here. Based on questions I've asked and the responses, a lot more of the devices can be rescued without opening them the posts suggests. And a significant number of those requests are because someone did something they shouldn't have.
From my experience, I have needed to restore an image three times now (plus a few times to experiment). Each of those times were because I did something stupid. Twice that was manually installing the wrong version on a device. I can't remember what the other one was, and I think that's because it would be more embarrassing. That experience is spread over my four devices and another six over the family. And five years. And it includes a lot of firmware updates.
Having said that, have a look at
Memory Upgrade Mod Guide for instructions. They are for the Glo, but the steps and tools are the same. As to the web portal mode you linked to, I haven't tried it. But, uses something that frostschutz wrote a while ago and there have been several reports of success with it.