Quick and dirty way is to export your whole user list, use that to get the distinct ID's and join them with your new property, and import that CSV back into Mixpanel.
In more detail:
- 1.
Export your user list from Mixpanel (just need the $distinct_id and $email columns)
- 2.
Open up that CSV in Excel or similar
- 3.
Open your existing list of emails in Excel too
- 4.
Use XLOOKUP or similar to filter the Mixpanel list to JUST the users you want to update
- 5.
Combine your CSV's (using XLOOKUP or similar) so you end up with a CSV with two columns: $distinct_id and your new property
- 6.
Remove the header line from that CSV (so the first row is the first user's $distinct_id and their value for your new property
- 7.
Import this into Mixpanel (Users -> Add/Edit Profile (right hand side) -> Import from CSV (right hand side) -> pick your file, and specify that your first column is $distinct_id and add a new property name for your new second column
