I'm using CryEngine for a game that I'm working on for a while but it is not an FPS (it's a Sandbox) then I would remove the gun and put another thing (example: a shovel)
Yes, it's possible to do this. You can follow the documentation found under First Person Weapons. The definition of such an item would be created using information found in the Weapon System documentation. Overall, the steps are as follows:
- Model a weapon/shovel through 3dsmax/maya.
- Make animations for the item through 3dsmax/maya.
- Export the item and animations using the CryEnigne 3 exporter.
- Make a xml file for your tool.