Pruning a Yucca by chopping the trunk in half!!

as from my previous thread, I've got a Yucca that's very deformed. I posted a question about lopping off the deformed branches, and I had a mixed bag of answers. Then I came acaross the link below:
I notice that the top of my Yucca has brown wax seal. It seems like I don't have much to loose by trying the pruning technique as suggested below, but I wondered if I should re-seal the top of the bottom branch, and if so, can anyone recommend what I should seal it with?
Anyone know why they are sealed? Is it to prevent branches sprouting out the top?
Thanks for your help!

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