Acid-Base Extraction

Lovely work friend!

I have a couple of questions if you don't mind. Is there a way to tell that 2 or more of the chemicals won't both form the Lewis acid with the hcl, rendering it useless for extracting one from the other? You just have to look everyone up? Will a weak acid be protonated by a strong acid ( for instance could an acetate be converted into a hydrochloride without first neutralizing it to the base molecule)?
When I read about A/B extractions, sometimes I read about chemist swinging the Ph to extreme levels, like 2 and 13. How do you know what Phis going to break a molecule, rendering it useless? At what point is it safe to say you have protonated/ deprotonated a molecule 2 points past the targets ph? 3?