@hightimes
The changes are being made to the device's region 140 which isn't a firmware region, it's a function-control region. All 24x5 devices with HWID 1371 use exactly the same firmware and apart from containing a "boot.bin" (really the ramloader), it only has the main system software, fw_all.bin, which is written to region 14 (hex: 0x0E). So, any changes to 140 (0x8C) won't be undone by a future fw update.

Regarding its potential to use ASR voice control: The 2455 is a 'junior' model. Because it doesn't have ASR or Bluetooth capabilities listed in its specs, it's unlikely to have a microphone factory-installed:
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That doesn't mean that it won't have a microphone socket or solder pads on the board for one because Garmin will usually use the same PCB for all models in a series. Therefore, you may be able to add a mike to any 2xx5 device as can be done in 37x0 series, see [Only registered and activated users can see links. ]. Note that you may then be effectively converting the 2455 to a 2495 and thereby cause TMC functions to disappear (see prominent warning in initial post of this thread). I don't think it's ever been determined exactly why 2495 loses traffic reception when region 140 is modified.