How can I add a data connection to an existing table?

I'm curious about this also. Is there currently a way to add a connection to an already existing table. Without having to use a workaround or creating an entirely new Table again?

Alas, no. 

My workaround was to create a brand new connected table, then use "import" on my original table - "Import into a table from another table" to pull over data from the connected table. You can save the import settings to match up the fields, so I go mash a button once a day to copy over what was brought into the connected table. It is faster and more consistent than uploading a file. (I have two backups who have access to mash the import button as well.)

It's not ideal, but I figure we'd have to spend a few years doing that every weekday before it would be more time than recreating my main table as a connected table. It has 405 fields, 25 relationships to other tables, and a form with lots of dynamic rules.

Good workaround. Note that automations can now run on the schedule and automations can run saved to table to table imports so you can set up an automation to run that import every morning around midnight.