[Scott R]

Windows can do this, 300k is not that big of a number. Just write a simple batch script like:

# START OF SCRIPT

# Declare input arguments.
var str dir pattern

# Collect a list of files matching the pattern.
var str list
find -f $pattern $dir >$list

# The list of files is in $list. Process one at a time.
while ($list <> "")
do
# Get the next file.
var str file, path, old_name, new_name
lex "1" $list > $file

# Remove path. This will give us just the file name in $old_name.
stex -p "^/^l[" $file > $old_name # After (but excluding) the last /

# Drop the first 7 characters.
chex -p "7]" $old_name > $new_name

# Insert MSG_IN_ after 14 characters.
chin "14" "MSG_IN_" $new_name > null # We are using > null because we dont want to see the output
# We want to insert MSG_IN_ into $new_name (thus no -p option).
script SS_SlashBack.txt ospath($file) >$file

# Rename $file to $new_name
system rename $file $new_name

# END OF SCRIPT


I stole this from another site because I didn't fell like typing it out, but this is a basic way to do it. You could of course then schedule it as a job inside of windows and have it run whenever.