Message types

Hi

In SAP for some of the standarad message types ,we can convert the message

type from "warning" to "error" or error to warning,if i want my own custom defined

text for that message type,where i can define the text for that message for e.g.

Message AA240-I want to key in my own text like user can,t change this particular

asset transaction type,pls change the transaction type or contact finance manager.

Thanks

Lily