Yup, as Jees said - high heat extended boils on mhrb are totally fine.

And personally speaking I'd skip the tannin/egg white, though is can make the mhrb brew a bit more palatable. To avoid much taste issue I will usually do my boils on the mhrb, then reduce down to about a shot glass worth of concentrated mhrb tea, then when I go to drink it I just throw it to the back of my throat, bypassing much of the taste bud locations [only hitting a few towards the back of the throat ime].