Modify EXIF time stamp for a batch of photos Based on Photos app data

TL;DR: How do I modify the EXIF time stamp and location information based on a modified meta data in photos.app? How would I batch this for all photos in my library?

I went through my entire photo library of my family and combined them all into a 20K image set. Many of these were imported from other cameras and default to my local timezone and/or have no location information. I painstakingly went through every photo and updated the time zone, time taken, and location information for every photo as necessary. As you can imagine this took a year to accomplish (spurred by iCloud Shared Photo Library). I now want to sync this image set to Google Photos.

This presents a several problems however because Google Photos only reads the EXIF data not the Apple Photos metadata and so has the wrong information. Many photos don't have a location (and Google photos doesn't allow geo coordinates by users), the time stamp is wrong, and/or the timezone is wrong (I have gathered that both apple and google photos base the timezone location on the geo tag of the photo and if there is no geo tag default to your local time zone which is often wrong as I lived in a different state for ten years).

The further complication is that if I update Google Photos to match the LIBRARY time stamp it considers the original in the photos library a different photo. Additionally I want Google to have the unmodified originals in terms of color correction and so if I edit the photo in Apple photos google thinks it is a different photo.

I really do not want to painstakingly repeat my geo tag and timezone corrections for every photo. How do I modify the EXIF data to match the metadata in Apple Photos Library for time and geo tag as a batch?

Postscript: I am doing this because I like the memories feature from both services and want to see it from both services.