Here's another way to do it that does not require changing the option prefix. From the help for Getopt::long

"To stop Getopt::Long from processing further arguments, insert a double dash -- on the command line"

So you can remove that "Getopt::Long::Configure" line from add.pl and call it thusly:

C:\>add --offset 6 -- -5
 result = 1

C:\>
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