"Replacing" Skills and Abilities

There's kind of a number of questions here regarding replacement.

First of all, I designed a custom Troll race. It works correctly and all except for one thing: my "Custom" Berzerker Training button doesn't replace my "Custom" Headhunter Training button in my Barracks.

Both buttons (which appear seperately in the Barracks, if both units are listed as Trainable, like the Orc Barracks) produce the same unit (i.e. Headhunters before the upgrade, Berzerkers after). Obviously, this doesn't produce a game-halting problem, but I would really like the Headhunter button to disappear and the Berzerker button to take its spot when the upgrade is completed.


Now, on a similar note, is there any way (preferably without triggers, but any trigger related solution is welcome too) to completely remove a skill and replace it with another one? What about in the case of Hero skills?

I want to make, for instance, a "fifth" level for the "Ultimate" version of each Hero skill my Hero has. Like Chain Lightning increases normally, but when you train it the fifth time, Chain Lightning is removed, and another skill (let's say a spell called "Lightning Storm" which operates differently than Chain Lightning) put in its place?

I hate to reply to my own post, but, would it work if I made a Hero ability for the same slot, gave it to the Hero, then disabled it upon map initialization - and when the Hero "learned" it, simply disable the old skill and enable the new one?