Hi everyone.

I have a skin cluster and I need to add some new joints.
somebody knows how to do it?
I think is easy, and the only way I think works, is by exporting skin weights, but the thing is isn´t working for me, perhaps I´m doing something wrong, anyone knows?
Thanks!

go to modify >> evaluatenodes >> and click ignore all and now add joits where ever u want by insert joint tool after finishing dont forgot to evaluate All under modify evaluatenodes

Hola!
Try to use Skin->Edit Smooth skin->Add influence (set Use geometry to false).
This command allows to add joints, meshes, nurbs curves to a skinCluster.
I recommend you to set Weight locking to 1. Otherwise weights  will be corrupted.

>> Alexander Zagoruyko
you forgot to mention that you must turn on lock weights, or else your predefined weights that you had worked out will be changed by maya, then after you added bone as influence object , use paint weight tool and onhold weight (remember to set weight 0 in add influence option box)