I did this mod to my H920+. The external H480 antenna kit works fine on the H920/H920+. The "without damaging anything" request might be an issue. You need to drill 2 holes in the sides of the lower case for the antennas, but I don't consider that "damage".
To use this thread, as the topic is the same. I'd like to add external antennas on my 920+. Where to see some Instructables on how to open the housing without damage, some connection diagram between the modules and so on?