I have been looking into it, but it is way more difficult to find this than you could ever imagine.
It is definately obfuscated, but I cannot imagine that this was intentional by designers.
Originally, I tried finding refrence to the the string indices for the caution. I am 100% sure these strings are the ones (I know because I modded the strings and it shows the changes on the nag screen). Here is that thread: printing strings from language (.LNG) files
0823: CAUTION!
0824: This product provides Route Guidance information for reference purpose only. Rev
0825: OK
(those are in hex)
However, I only find about half of the strings im looking for referenced in the code. There are many strings (including) these which are using some other method (perhaps loaded by reference in Navi.rff menu file, etc?). So this has become a dead-end.
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Anyhow, one interesting note, which is the current route that I am investigating, is that when there is an active route, the unit will bypass the warning screen and go straight to nav screen on startup.
I see this happens when USER\RW\PATH\ROUTESTG.DAT and USER\RW\PATH\PATHINF.DAT are present, and have the right flags/settings to indicate an active route in-progress.
So the next trick could be to try to determine what in these files indicates active route and then look for something in Navi.exe that is triggering this.