With FAB3K you can easily flip/swap all PCB layers (i.e Top to Bottom), plus internal metal layers symmetrically. Perfect for optimized PCB Panels and more. The command is called: Swap Layers
Afterwards FAB3K will take care of everything. Then export to any format like: Gerber, NC, ODB++, IPC-2581, DXF, 3D Step, and send out to PCB manufacturing.
Here's a quick tutorial movie (no sound):