
I just want to add new device UDID to an existing provisioning profile, to mod
Go to the devices setting in https://developer.apple.com/account/ios/device/deviceList.action and see how many devices are added in your account after that add the additional devices UDID and save that.
Now when you come back to the provisioning profiles then you will see the devices you just added. You can select all the devices and then press generate. Now you can easily download the updated provisioning profile.
Hope this helps.