1. Download unpack/pack tools from Rick: http://svn.gib.me/builds/dunia2/ (last dunia2-r51_b39)
2. With Gibbed.Dunia2.Unpack.exe unpack files worlds\fc3_main\fc3_main.dat/.fat, common.dat/.fat, patch.dat/.fat. This is sufficient for editing a single.
Help:

Usage: Gibbed.Dunia2.Unpack.exe [OPTIONS]+ input_fat [output_dir]

Unpack files from a Big File (FAT/DAT pair).

Options:
-o, --overwrite overwrite existing files
--nu, --no-unknowns don't extract unknown files
-f, --filter=VALUE only extract files using pattern
-v, --verbose be verbose
-h, --help show this message and exit

3. Find and edit the files.
4. Add the edited files in a folder with the unpacked patch.dat/.fat 5. Pack the new patch.dat/.fat with Gibbed.Dunia2.Pack.exe (that is, it must contain all the original files from patch.dat/.fat + files you edited)
Help:

Usage: Gibbed.Dunia2.Pack.exe [OPTIONS]+ output_fat input_directory+

Pack files from input directories into a Big File (FAT/DAT pair).

Options:
-v, --verbose be verbose
-c, --compress compress data with LZO1x
--pv, --package-version
package version (default 9)
--pp, --package-platform
package platform (default PC)
-h, --help show this message and exit

6. Copy new patch.dat/.fat folder data_win32\ and play =)
P.S.: At the moment we know 53% of file names, other names are unknown, but they can also be edited, but they have to stay in your __UNKNOWN folder