Building Metamorphosis?

Specifically, what I'm looking for is to pursuade buildings to show one of the 'summoned unit' timers, without having to substitute an entirely different building (as I have several triggers listening intently on the unit,) and preferably with a minimum of unwanted side effects. I've shied away from avatar because of magic immunity. Metamorphosis can be rigged to have no side effects whatsoever, but it resets the building to it's construction phase. Storm, Earth, and Fire seems unlikely to work. I'll be trying out polymorph, but if anyone has experience with this sort of thing, do let me know.
Thanks,
Alfryd.

I've tried that, but it doesn't seem to be having any effect. All the abilities are removed too (and I made sure they're present in the alternate form unit,) so I assume it's not a purely 'cosmetic' thing.
In addition, I seem to recall the same problem cropped up once metamorphosis ended, and as there's no exact trigger for telling when a spell's duration ends, I'd have to sort of guess using timers when to apply the animation. I suppose I could remove the ability just prior to it's ending, but that might mess things up badly, and it's a pain anyways.
I don't get this problem if I uncheck the 'is a building' box, but then, of course, I lose the building pathing map (though, oddly enough, it keeps the ground texture.) The pathing map has to be provided by another unit with no model directly underneath, which, again, is a pain.

Yes, I can do a periodic check, but if I'm even, say, half a second late, there will be an interval during which the 'birth' animation is visible before I can reset it, which looks distinctly unprofessional, so to speak.
Also, I suspect that the ability removal has to do with the fact that a buildings abilities don't appear until construction finishes. I could be wrong. I'll check it out.

Or do like this:
Make a berserk ability without any stats ans when you use it u do this with triggers:

replace building with buliding (alternate)
add a water elemental countdown timer for ordering/casting unit.

w8 <the time u want>

replace building (alternate) with building

Change the buff for the water elemental so the text match what u want!

Wait... wait... how do you add a water elemental timer to a unit? I don't want to have to replace the building because I have triggers listening on it that would need to be reset.

The problem being that a polled wait will often last slightly longer than the specified duration, so, again, you get the problem with animation 'flicker.'

I use a Mac. Macintosh .mdx editors worth speaking of are somewhere between few and none.