Convert a Connected Table to Normal Table

There is no way to add records to a Connected Sync Table. 

but super easy to disconnect.

Table Settings
Google Drive Connection and click to disconnect.

but once disconnected you cannot revert to connected.

so for sure fully test you alternate method on another normal table first. 

You can probably Copy the table to test and get all your fields set up.  Go to the Table Home page in old view and use the More... button.