To answer your question, there is currently no tool that is released (or I'm aware of) that can edit an efp file completely.
Now, If you mean as in making a completely new .efp file, then it's gonna be a lot of work to do.
First, you will need to grab a .efp file you would like to edit, use a hex editor to open it, find every mesh(.bms) in there and change it to the .bms you want(along with the ddj file for that bms). If you want it to move around (animation), then you will not be able to do that directly, a workaround would be to find an efp file that has the behavior you want, so if you want to make an efp file that spins around, try to find an efp that already exists which spins around, change it's models and textures, and you will be good to go.
An easier way to do all of this would be using skilleffect, you can play with it a little to make it act like you want it to, but it would only work in certain stages(for example skills, avatars, items, etc..)
Good luck ^^