Yes, this is possible by editing "WorldAreas.dat"
There's a flag for each area that controls whether or not the minimap is fully revealed
If you were to go through and set that flag for each area, the game would then show the minimap as being revealed
You can also achieve this through memory/client modifications, but you've asked for the ggpk modification approach
Here's the reference point for the current 3.13.1.9 client that just updated tonight:
Screenshot - 680e2e9e8d708cbc50a9480bfe1a0a46 - Gyazo
You would have to go through and hex edit offset 0xCB of each WorldAreas entry with the 4-byte int value of 2 to achieve the minimap reveal
Each WorldAreas entry is currently 0x2C0 bytes, and the size of this struct tends to change each major update, so you'll have regular work to do
.dat files have a specific but simple file format as well, so I'm just generally telling you what to do, there's more work involved to actually do it
So, I'll leave the specifics of editing the dat file itself to you, as this method is pretty cumbersome and takes a bit of effort vs trying to just modify memory or the client itself.
I at least wanted to show you the method is possible though and how you can make it work.
GGPK file modification since the filesystem change is pretty inconvenient though, but still possible if you're willing to jump through the extra hoops.