Processing rule option to be able to run a script against values

Have a need to decode values being passed and think having the ability to run scripts as a processing rule option would be beneficial.

Today there's the abitlity to set a Custom Value but it would need to match, which with endless numbers of possibilities makes this it not an option.  My suggestion would make it so variable content could come in and the script define what need be done to the value... such as decoding.