Hello
Hmm maybe there is but before you make any changes with any files don't forget to backup the stock textures!
There is a tool provided in FS2004 terrain SDK called imagetool.exe or another nice program DXTBMP both small programs can resize/convert the images used by fs2004, imagetool is easy to use you open the file and then click save as from the file menu and you can save as dxt1,dxt3 formats.
Remember to backup your textures before you proceed any changes :mixedsmi: