mapping section in REST Web Service Listener Policies

Hello,

I need to create an event attribute by using a field from the source event. 

For example:

Source Value: [<*>X1<*>ABCD]     -> Target Value : XYZ

Source Value: [<*>Y2<*>ABCD]     -> Target Value : QWE

Source Value: [<*>DEFG]               -> Target Value : ASD

Source Value: [<*>ABCD]               -> Target Value : ERT

There are 30+ event rules.  So i want to create a mapping. Is it possible?