I doubt that the conversion is firmware related. The same firmware is used for all aera 5xx (500, 510, 550 & 560), Therefore the differences in operation between the models are either regional versions set by 'Locale' (unlikely in the case of 500>550 however), or, more likely, the enabling and suppression of available features are controlled by a flash region. In other Garmin devices, this has been achieved by using a modified splash (the 'logo') in rgn16 particularly in earlier devices, e.g. 1xxx. In more recent devices, the functions are controlled in rgn140. The first thing I'd do is dump both those regions, but before you do you need to have a basic understanding of dumping (copying) and writing to regions, so read this thread: [Only registered and activated users can see links. ].

You'll need to dump those 2 regions, look behind the spoiler:
Spoiler:
First, let's check for sure that it's not an RWFS device which from memory I'm fairly sure it's not. Tap the speed field on main page to see the Speedometer. Hold the speedo for about 5 seconds until you see a hidden menu named 'Diagnostics Page'. Scroll down to see if there is 'RWFS Setting' entry, if there isn't use these commands with the appropriate Ldr.bin:
rrgn,16,1:/16.bin
rrgn,140,1:/140.bin
reboot

In the event you do see 'RWFS Setting' in the menu substitute "2:/" for "1:/" in the commands.

Report further and post the region dumps (16.bin & 140.bin) when you have them.


If you're in any way unsure about how to do the above, post that and I'll make you an SD kit to use. Using a wrong Ldr.bin (boot.bin) could hard-brick your devices so be careful!