There is little chance you will destroy it, unless you hammer it with a brick, with is not in the instruction list
John's instructions are fairly foolproof and specific as to what to do. Following the instructions exactly as written lessen your chances of any problems. John Clark is an aircraft pilot... he is, shall we say, sorta used to following checklists to the 't', and his instructions on this forum normally follow that high degree of exactness. However,
if you were to freeze it or not succeed in rebooting, there are wipe and restore applications for that purpose.
As always, backup your current device before doing any OS adjustments, upgrades or reloads.
And, always at your own risk (of course, you've got 150,000+ members here to back you up if you need assistance).