Edit April 9, 2013
Apple responded to my bug report on this issue and said that "the problem is fixed." I confirmed that the problem has been fixed. Now I can add devices to older Ad Hoc profile profiles that were created before the website was updated.
Now the problem is resolved.
Note: underscores ( _ ) are no longer allowed in the names of new provisioning profiles.
As of the previous weekend of April 6, 2013, it is not possible to add devices to my existing Ad Hoc profiles for development on Apple Developer Certificates, identifiers and Profiles .
There are a lot of questions at StackOverflow that describe how to add devices to iOS Ad Hoc profiles, and it was a pretty simple task until this weekend.
I can still edit the list of devices for my development profiles.
Can someone tell me how to add devices to my Ad Hoc Provisioning profile on the new Apple Developer website?
Notes:
- This is definitely an Ad Hoc profile, not an App Store. Distribution profile.
- It is not possible to take a picture using the switch below: "iOS Distribution ...".
Change iOS firmware profile Screenshot: 
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