Both 590 and 595 have 3D Terrain feature as standard anyway:
Code:
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The method described in the GPS-Expert link is a full conversion to 595's HWID of 2436. A somewhat safer way to convert would be to use the original 590 boot.bin combined with the rest of 595's firmware to make the conversion, if it can boot the 595 firmware it should work like a 595 and that way you can keep the 590's HWID of 1796. Provided it does work OK it will give you a smoother way back to 590 should things go pear-shaped. Whichever method is used, it's also a very good idea to backup the unit's nonvol memory (probably in rgn154 for them) before and after the conversion: [Only registered and activated users can see links. ]

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Seeing both region layouts are the same a full conversion is probably quite safe but best to backup nonvol for sure.