I'm still kind of confused. I sort of know how to apply animations to bones, not the other way around. And saying to add the bones to his animation is also confusing considering that Goku's entire .ean is composed of many smaller animations. Which of his animations would I apply them to?

I'm also having an issue where the <indexBone1_notIn> command refuses to actually exclude the bone indexes that I specify; it still puts all of them in the bone filter.

EDIT: Figured out the <indexBone1_notIn> issue.

I think I got it! I managed to get the tail animation on Vegito's standing animation   But as you said, that's only one of many, MANY animations, but it's a start, right? 

Why would you want to edit the cms when you already have an editted ean?
Edit the ean and everythink will work, no need to alter the cms.

I really don't have all the answers you may need, and to tell you the truth the ean organizer is not necessarilly my strongest topic. I discovered the inital steps on how to add a tail to an ean that didn't have one, but when I saw that the tail is working I lost interest, I never completed it. I told the others how to do it and was done with it. Since then Olganix improved the organizer a lot, I should catch up on what he did myself before giving you more advice
UTtank aka SuperHuman and Komodo have worked a lot more with the organizer now than I am, so if you run into issues they are better suited to help you out.

this is my go-to reference for tails

Load VG4.ean
Load HUM.ean
AddAllBoneInFilterFor 0 120 121 123 124 125 126 127 128 129
CopyPasteRange_WithBoneFilter 1 0 0 81
Save 0 NEW.ean

This is super simplified, and only accounts for aniamtions with the full index range

Let's break this down, first "AddAllBoneInFilerFor"
Here we are selecting every bone for the source file that you are not okay with replacing
the range I found for the tail bones is unique to VG4, 120-129

to find this range type GetBoneList 0

You're looking for the index number (left) of each X_Tail bone (9 in total)

So lets say they are 110 - 119

AddAllBoneInFilerFor <animation index of the tail source> 110 111 112 113 114 115 116 117 118 119

Now, CopyPasteRange_WithBoneFilter -- this is the fastest command possible, it copies and pastes a range of animations by index with the bone filter (every bone apart from tails)

The animation source is 1 in this case so we're really just copying the body animation on to the tail animation

I used the full range animation range (0-81) because VG4 and HUM both have no exclusive animations (most will for skills) so you have to copy and paste around them with basic commands

Then we save the tail source as the new animation. Because you cannot copy bones that don't exist, you have to copy everything else into an animation WITH these bones.

If you need to put a tail on a skill animation that you plan to keep, CMN.tal.ean is a great source for tail animations if you can use that, if not you may need a blender edit to fix the animation length to match the skill.

Alternatively, there is probably a tailed version of the animation for Frieza race somewhere that you may be able to bonefilter on to it.

I kinda skimmed over this because I'm very busy, but I hope this is what you're looking for. If you need to use this with someone else's moveset (if the animations don't match) use mugen's CMS (?) editor and set BAC and BCM to "../XXX/XXX" <--- where X is the desired skillset and leave everything else as is