1) if this is on the same server, just open the report in ReportWriter and Save As with a new name, and then make your changes.
2) if this is not on the same server, find the file (it will probably be in %PROGRAMFILES%\solarwinds\orion\reports) which ends in .OrionReport and just copy it. Then edit your copied version.
IF you are on the same server, but have two different customers who should not see each others' reports, then under %PROGRAMFILES%\solarwinds\orion\reports create two sub-directories: \customer1 and \customer2 (or whatever you want to call them.
Then put ALL the reports for each customer (custom or standard) in each directory, and modify their account(s) so that they use the new sub directories.
Hope that makes sense.