You shouldnt have any problems if you are doing a staged roll out.
In any event make sure you do a backup of the running Configuration of the CME, and also the CUE before you proceed, this will assist you to bring your system back online if something was to happen to the configuration during the upgrade.
Then before proceeding to the other sites, make sure you follow the same proceedure, and also ensure you do proper planning before moving full steam ahead, proper plannings a smooth roll out.
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