Assuming you mean to use thdat, the command is 'c' followed by the game's version ID. You can view this by simply typing "thdat" without any parameters - it'll show its help.
Usage: thdat COMMAND[OPTION...] [ARCHIVE [FILE...]]
COMMAND can be:
c create an archive
x extract an archive
h display this help and exit
V display version information and exit
OPTION can be:
# # can be 2, 3, 4, 5, 6, 7, 8, 9, 95, 10, 11, 12, 125, 128, or 13 defaults to the latest
Report bugs to <xarnonymous@gmail.com>.
Example:
thdat c8 output.dat inputFileA.dat inputFileB.wav etc.etc
You need to specify all files to include in the archive; AFAIK it's impossible to simply replace files within an existing archive. So make sure you keep everything when you unpack that thxx.dat/thxxe.dat file or you won't be able to rebuild it again afterwards. If you're missing these files though, you can just re-extract everything, replace the modified files with your own version, and repack that.