what after 100% regenration ? it stops or keep mounting .

High as you like. The master robes give you +150%. After you tune the wells for the College, your regeneration is so high for a time you can cast spells constanly.

What do you mean tune the wells in the collage?

its not for me its for azura she have the mask of 100% magica reg and glass armnor plus jewelry .
so i wanted to know if doing more magica reg enchantment will do any good

That's what the Highborn power does too. It goes as far as you want.