yes it´s like Flintlock1415 wrotes, spells - attach kf - select kf (the kfm only says the game which structure [nif] and which kf is for which situation). But like said before with your nif it won´t work atm, because the lee model is outside the tree of the animated bones [you will only see a moving skeleton].
To get it working with lee, open the nif, rename the bones the model is rigged to (best uses NiSkinInstance of the NiTriShape of lee), save. Open the saved nif 2 times, in one (now called target nif) delete the entire scene root part of the tree with the model (not the one with the animated bones). As last step copy the model from the second Nifscope instance to your target nif and add it as child to MD NonAccum.
Btw, imo it´s worth to invest the time to get familiar with nifscope, reboning it´s much faster with nifscope than with nifviewer (but tbh depends on the similarities of the bone structure). Eg if both models have the same structure (and bone names), you only have to copy the exported model to the nif which animation you want to use