Adding new weapons to game or changing existing model

Hello All.
Are there any tutorial about adding new weapons or changing existing models.
I made some realistic sabers for game but stuck wıth cgf. fıle format to make changes. As well as ı trıed to export the cgf fıle
and made some changes on model then agaın to convert to .cgf ıt was successful but when ı open the game changed model was lıke 2d and totally wıthout textures. Can anyone has any ıdea for work arround. ?

Also, what 3d program do you use?

Thank you for the link i am using cınema4d and created my obj. files with it

I know that some people (and me) used CryBlend converter for Blender but that did not export material info so the item was without texture as well.
The materials in KCD uses option for 2nd UV map (unlike the original CryEngine) and maybe it is the reason the ordinary cgf do not work properly.

It seems that so far the only way is to have the Max with the plugin provided.

Thank you i will try max as well. I wonder if is it possible to use current model and just play over it without adding anything to model plus keeping the textures.