To edit and hack the narc files, you need to have the NarcExplorer 2.
Compatible with: Pokemon Diamond, Pearl, Platinum, Heart Gold, Soul Silver, Black, White
Supported OS: Windows
NitroExplorer 3 is the advanced version of NitroExplorer 2 – the tool that can extract and edit ARM9 with various overlays.
Nintendo Pokemon ROM Editor (NPRE for short) is a strong tool for editing and hacking any Pokemon ROM on the NDS system.
If you think your overworld is too small or too big and want to resize it to your conditions, use Overworld Changer.
Not only Pokemon FireRed can be hacked, adjusted with a tool but also Ruby – Sapphire – Emerald – LeafGreen… all the games of Gen III.