data migration using extension setting service

If you've only used feeds created by the AdWords user interface, you can use extension setting services immediately.
However, if you've created custom feeds with the API, you'll need to first perform the following steps:

Allow me to confirm(double check), as long as I have been using the legacy feed service to create feeds, if I decide to switch to extension service, then I have to migrate all data to extension service, and I lost the ability to operate them using the legacy service. or I can migrate back ?

 

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