Presumably, each "dynamic" page is being generated from data stored in one or more database tables, triggered by some identifier in the URL that tells the PHP code which data to extract and output. In order to customize that output, you would likely need to add/modify DB tables to store that custom information, and you would likely need additional PHP code to make the determination that such data exists for a given page and then determine where/how it needs to be output. Not likely to be rocket science, but not necessarily trivial, either (depending on what your ultimate needs are, how the app is currently coded, and how clever the developer is).
It certainly, at least on the surface, does not sound anywhere near "impossible", but depending on all the details and variables that currently are not known to us, whether it is feasible within your current budget and schedule restraints is something that can't be answered yet.