If you are getting crazy trying to find the save as button in Mari, don’t worry, it's not there.
The best way to save as in Mari is using snapshots tool.
Is not exactly the same as save as option, but is something quite similar.
- In this example I have a version of the robot with some flat colors as texture maps.
- Open the snapshot window, under view -> palettes -> snapshots.
- Create a new snapshot and name it as you want. For example v001
- Keep working on your textures, channels, shaders, etc.
- When you want to save as indeed going to file -> saves as (traditional way) go to your snapshots window and create a new snapshot.
- If you want to switch between versions just select the thumbnail and click on revert.