Hello,
When changes are done in a given Message Class that don´t rely on Original System (Standard SAP or even Customer) and you need to maintain Long Text, the Create Modification dialog appears.
Basically you must enter a name from customer namespace (Starts with Y/Z) in "Modification Name" field and then choose Original Text for "Template Type" field.
For further details see SAP Note 989653.
Then you will be able to enter Long Text for your Message modification. The following picture shows the template for Long Text (in case you need it).
Image may be NSFW.
Clik here to view.
Best Regards,
Sidney Gubany
