Please give the author of AbapcadabrA the chance and opportunity to explain why standard SAP should not be copied into custom developments...
Adapting a report is generally not a good thing to do. When making changes to SAP the developer should always try to find ways out or at least minimise the number of changes.
Well, when report adaptations are the issue, the easiest way would be to copy the report, and change the copy. But even then, the altering the SAP reports can very easily become a very complex job. The SAP reports are set up to cover a wide variety of variants, sorting methods and lists of exceptions that will be taken into account. Most reports are geared up to cater for a lot more than a single customers needs.
All I’m trying to do here is discourage you to actually do changes to any standard SAP report, or even copy of a report. It’s a total-loss situation, don’t fix a car if a the car’s value is less than the bill of fixing. What ever report a developer has to do, it should be completely understood at some point. Developing a report from scratch can be seen as a very effective way to achieve that. Set up the specification and mention "... which should look like the existing report in SAP", and have development invent their own solid, strong, wheel. Liable to opinion though !
Other than becoming complex, copied developments have the tendency to no longer work after a release change.
Luckily SAP has come a long way and they have come up with excellent solution alternatives. Implicit and explicit enhancements, the enhanvement framework, in effect you can apply your changes to the beginning or ending of any routine, function module or method through the enhancement framework. Don't let this be an open door to changing whatever you can find though !.