Add bones

Can I add new bones to a model on Blender? And how do I write it on the qc file after?

What do you plan to do with these new bones? And on what model, as in: is it a pre-existing model in gmod or one you’re working on / porting?

You can very easily add a bone to an already existing armature in blender (in edit mode, having the armature as the object selected, you can extrude [E] new bones from an already existing bone), but depending on what you’re planning to do with it you either won’t need to do anything in the QC or something that’s likely out of your scope.