Can GP Hooks be used on some pages and not on others?

I've been looking at the GP hooks add-on. It looks as though it's designed to insert code and content into the web site on a site wide basis. Does this mean it appears on every page of the site?

Is there any way of inserting code and content, but on a per page basis?

For example, say I want to insert Adsense onto 10 specific pages of my site, and not onto every single page.

Is there a way I can install the code (into a Hook?) onto those 10 pages, and then fill it with code for a 300x250 sized ad. Then, at a later stage, I can remove 300x250 code from the Hook and insert 728x90 code so that it will change the ad on all those 10 pages in one go?

Thanks,

Will