Hi annanc14,
welcome to the Apple (user-to-user) Community!
Re: Is there any way to change the pronunciations of words in Spoken Content on a Mac?
Sorry, I don't know for sure ... seems if you use VoiceOver the built-in screen reader for macOS, you may have more control than in Spoken Content:
Eg: You can use VoiceOver, to hear descriptions of every item on the screen and to control your Mac using the keyboard. See the VoiceOver User Guide.
You can use the Pronunciation pane of the Speech category in VoiceOver Utility to customise how VoiceOver pronounces text and symbols.
See how to use: Pronunciation, Speech category, VoiceOver Utility on Mac - Apple Support
All the best :-)