Normally used for modifying the SAP standard programs.

With Modification Assistant on, you can only make modifications to programs from the ABAP Editor using the 

Edit -> Modifications operations -> Insert, Replace, and Delete line area or pushbuttons. 

In the Modification Assistant, you can make all customary modifications to Repository objects.  If, however, it should ever become necessary to disable the Modification Assistant (for example, when uploading a program to the Editor), choose the 

Edit -> Modifications operations -> Switch off assistant menu function for the appropriate Repository object. 

Only make this sort of change after considering whether or not it is absolutely necessary and thinking about the consequences that such a change will have during the adjustment process. The system will register the fact that there are modifications, however detailed display of the modifications will not be possible since the Modification Assistant will have been disabled at the time they were made. Modification adjustment can only take place during an upgrade using 
version management functionality. 

If you want to undo the modifications you have made to certain Repository objects, you can do this on the initial screen of the corresponding ABAP Workbench tool using the 

Edit -> Modifications operation -> Undo modification function. 

You may also undo modifications in the Modification Browser (SE95) by selecting the Repository object and choosing Reset to original. This will reset the entire Repository object to its version in the standard.

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