Something like this will do it. The for
loop may need to be modified depending on which filenames you wish to capture.
for fspec1 in DET01-ABC-5_50-*.dat ; do
fspec2=$(echo ${fspec1} | sed 's/-ABC-/-XYZ-/')
mv ${fspec1} ${fspec2}
done
You should always test these scripts on copies of your data, by the way, and in totally different directories.