Feature classes that belong to different datasets may have different extents. These feature classes can be appended under one dataset with a new extent. One way of doing this is by exporting the feature classes into shapefiles, importing them into the new dataset, and exporting and importing them again using "sdeexport-o create" and "sdeimport -o append".
1. Export F1 to a shapefile using ArcCatalog.
2. Create a new dataset, D, with a larger extent.
3. Create a new feature class, F2, in the new dataset D and load data into it.
4. Import the shapefile (feature class F1) into the new dataset D using ArcCatalog.
5. Export one of the two feature classes, F1 or F2, using the ArcSDE command line "sdeexport -o create".
6. Import the exported file by appending it to the other feature class using the ArcSDE command line: "sdeimport -o append".