yes it is and no you don't!It's not very easy as you need to extract boot.img from the full oos zip(or extract it from your phone with fastboot), patch the boot img, then fastboot flash it back. Far more simple to to it as explained. And you need a computer anyway.
And with the new slot A/B architecture you need anyway a computer each time you flash a ROM, as you need to reinstall TWRP each time, due to the lack of recovery partition here (it's been 'replaced' by vendor partition necessary for Treble compatibility) .
First up, yes, this was posted last year, and no, I haven't read ALL of this to realize whether you've been refuted, and it would be unreasonable for you to expect me to have done that.
Let's try not to spread false info. If you don't know, like many times I haven't been up to the given challenge, I make sure to include a disclaimer as to how "strongly believe such and such, but in all honesty, I'm not a hundred percent sure!" type of thing.