there is some customisation possible, but this is mainly based on numbers - you can add a count of virus scans, or the number of times that an event has happened, but not add information like that.
There is a script that will check the mailbox size. You could create a script log entry if this is over a predefined size (say 10gig), then use the exec report to count the number of "mail is over 10gig" messages in the script log, for example.
LANWorxYou could create a script that will get the contents of the txt file, place the contents into a variable and then plaster this into the script log of the agent. From here, you should be able to report on it.
Hope that makes sense,