In many projects I've seen using ASMA attributes, usually to retrieve the name of the file or the server from which a file have to be picked up. Every person who has used them at least once know how difficult could be performing unit testing for those attributes, especially in the early stages of the development when you don't have any real file or you cannot upload anything on the remote or local server for testing.
Recently I have discovered the possibility to Edit Messages in error directly from SXMB_MONI, by typing the command 'edit' in the command menu:
This will bring you to the web-based editor where, if you have the permissions (given by role SAP_XI_MESSAGE_MODIFY), you can edit the payload of the message and save it for re-processing:
The interesting feature is that you can edit also the additional attributes, like the dynamic configuration, in the same page:
Once saved, you can re-process the message in SXMB_MONI and get the desired result inside dynamic configuration 
Of course, message editing is not encouraged in production systems unless really required and roles must be properly setup to restrict it.
Have fun!
Antonio