Yes, it is, although "add" might not be the right word. Since it has only 2GB of internal storage, and no provision for an external SD or uSD card, you will need to store your existing map offline on your PC before you can load the US map onto the unit. Given your location (had to peek at your IP address since you did not specify), I assume you now have the UK/ROI map only on your unit?
We can advise on safely backing up your UK/ROI map to your PC so that you will be assured of the ability to restore it later.
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