If you Doing some updation in sites will it effect your PR in any manner changes like adding a new page, modify design on home page etc ?
PR is always for the webpage and not for the site. Nobody knows how Google calculate the PR and it depends on the back links at the webpage and W3C recommendation too.
if u change particular content, which ranking and due to that ranking lost then it might affect your pr
If the main update does not change amount and quality of links placed on that page , I mean some techniques like keyword farm or too much cross linking within a site , or put too much links on one page which reduce the quality of the site as a whole , I think it's not affect the PR.