I am inheriting a Wordpress site where the page names in URLs are very descriptive things like page_id=81. Is this something that I can change globally or do a simple search and replace on?
By default, WordPress uses a query variable structure for URLs because it doesn't know for sure whether or not your system supports URL rewriting. But if your server does support rewriting, you can enable Pretty Permalinks.
Basically, pages change from
You can adjust the settings to use whatever URL structure you need on the Permalinks page within WordPress. So yes, it's something you can change globally.