I’ve put together a quick Shortcuts shortcut that should help you do what you after with a bit of modification to suit your specific requirements.
Sharing an ICS file from Safari isn’t working for me on Shortcuts at the moment; the share sheet options appear but are non-functional. Maybe a reboot or updating to 14.5 will help, but I have also set it to allow manual entry, defaulting to the clipboard when run standalone, and copying the URL does work.
You can choose whether to get it to do partial or full matching on the event title (/summary), but I’m hoping this will give you the gist to get started, and like @Tjluoma noted, it is a plain text file format, so if you treat it like text, you can more or less do anything you like with the data. I do that with contacted version (vcard files) as Shortcuts doesn’t surface all of the details from the file format through the user interface.
Now, as it stands, you can’t modify the content at source, so the shortcut/approach above is modifying it in transition. But, you also have the option to transform it at destination, once it is in your calendar. You could have a shortcut you run periodically (manual or scheduled) that picks out any events that match your desired event title structure and modifies the event title. This would save you working with ICS files and allow you to only have to work with calendar events (and share sheet/clipboard copied URLs, etc.)
I haven’t included a shortcut for that as calendar event filtering, loops and editing should be all that is required and is relatively straight forward I think; but if you want to pursue this and need additional pointers, they can be provided
Ultimately, you can decide for yourself which approach matches best to your own comfort level and is optimised for your needs.
Hope that helps.