How to manually link existing records for Salesforce-to-Salesforce?

My Salesforce-to-Salesforce set up and working (with automatic sharing etc). It works great for go-forward records. and struggling to find out how to deal with existing records that exist in both orgs. As an example, if I spin up 2 brand new Dev orgs and connect them with Salesforce-to-Salesforce, I end up with duplicate "Edge Communications" in the Partner org. I want them to be the same (not looking for real-time fuzzy matching, I'm ok doing the work of linking them individually)

How can I manually link the 2 accounts together? I'm looking at the PartnerNetworkRecordConnection docs and see that there is PartnerRecordId, though this field is not writeable.

A bit of background We have an old crusty Salesforce org with a bunch of complex integrations set up. We are building a nice new shiny org that we want to be the go-forward place to do things. As part of our migration plan, there will be a period of time where Sales will be working in the shiny new place and we can't just move over the integrations, thus S2S to push over just what the integrations need in the interim. To make this work, I think we will export from the crusty org all the data, and import into the new shiny org the cleaned-up data. We can maintain relationships as needed etc to help with the problem I have posted about.