You can copy them 1 by 1 only ^^
This will overwrite the custom data starts from 0000.Or using Import All Object Editor Data at Object Editor.
Add notes that users needs JNGP for this, and it's broken on one of windows latest patch (Windows 64 Bits?).I heard you can Import All Data at once by using LUA Scripts, this is how they manage to do the Bonus Stats system without forcing the user to either copy paste 1 by 1 OR Import All Data using the default feature - this will overwrite Custom Data inside your imported map.