I have oscommerce shop which needs to be modified to this:

mainpage is index.php, is just hardcoded stuff in, so can be used seperate from the original index.php where all ocommerce stuff is in.

so the main page would load faster because of this (is no rubbish in)

the separate page can be remamed to lets say example.php, and all categories_listing.php and product_listing.php is directed to example_product_info.php for example.

i have already a function like this in other sections of the shop

Its not comlicated to do i guess, its just separating the diiferent php sections out.