Since the new User Profile Batch Update API is not available on all tenants yet I have been using the “User Profile Bulk Property Updater” from the OfficeDevPnP samples at https://github.com/OfficeDev/PnP/tree/master/Samples/Core.BulkUserProfileUpdater
This bulk updates user profile properties in SharePoint Online through the use of a CSV file.
I am a big fan of Office 365 Developer Patterns and Practices and this sample is so usefull.
Here is the input format for the CSV fil to update your profiles with hiredate and birthday:
UserName,SPS-HireDate,SPS-Birthday
i:0#.f|membership|atestusr03@unclouded.onmicrosoft.com,01/05/1971,12/04/1971
i:0#.f|membership|atestusr01@unclouded.onmicrosoft.com,11/08/1975,11/22/1975
i:0#.f|membership|atestusr02@unclouded.onmicrosoft.com,12/21/2012,07/03/2012