Ok, I just performed the operation with a minor emergency. And same as the guide says I advice to really discharge the battery and have a contingency plan in case of puncturing it. Freeway to the yard or another place that it can safely finish ‘boiling’.
I tried to be careful, but the adhesive used by the producer is so strong that you can rip the battery cover just by an attempt to lift it. I was not patient enough and got a boiling battery. Found remained functional luckily, but it was a close call.
Also what I will do next time is to wear protective glasses.