All of which brings my to my tired question (revised a little each time). And I ask again because this part is still not clear. Assuming that the files are already backed up, does not this simple line:
 
%perl -pie 's/old/new/g' ./*/*

 
It comes close ... what this line does not do is act on the files of the sub-directories of your sub-directories. Wih your original method, files in the current directory and its immediate subdirectories are being acted upon, but no further. No files in subdirectories therein would be acted upon, negating the 'all sub-directories' requirement of your one-liner. Depending on your directory structure, this could leave a large number of files untouched.
 
The best way to describe this is through example. From the /usr directory of my mail server:
 

budapest:/usr# ls -l ./*/* | wc -l
   4505
budapest:/usr# find . -type f -print | wc -l
  22838
[download]

 
The difference in number of files is quite apparent - If however, you have no further subdirectories beneath those of your current directory, then there should be no problems, but if there is, potentially a large number of files could be missed.
 

 
Ooohhh, Rob no beer function well without!