Re: just how hard is it to change the front glass on a galaxy note 4
If you've done it before (on any phone) and you have a heat gun with good temperature control, fairly easy.
I've found that it takes most techs between 6 and 10 phones before they can do it without damaging or overheating the screen (which is why many shops keep unrepairable phones, to use to teach techs how to do things like replace the glass - you can't kill a corpse).
As belodion said, the chances are that you'll pull a glass piece when it's too cool, ripping the screen, or you'll overheat the screen. Either one will mean that you need a whole new screen, which will cost you more than paying a reasonable shop to replace the glass.