IIRC this type of thing, whilst very very tempting, has some weird drawbacks in the "Oh, and I don't have the mana because I spent it, spell fizzles - except it doesn't hahahaha!" department. (It's the floor above menswear)

You don't RC. This works fine. (Cf Root Sliver and Vexing Shusher.)

Good point. I find it somewhat amusing that the oracle text for root sliver still says "Root Sliver can't be countered" but had to be updated to add the "by spells or abilities" clause to "Sliver spells can't be countered", presumably because at the time it was written, all Sliver spells were creatures which never targetted, but eventually Nameless Inversion et al were printed, as Sliver spells that did target :)

Holy... I never realized changeling instants could work with Slivers. Hmm... you can also make the spells colorless and gain protection from a color. It's a pity none of them deal damage... otherwise we could play with lifelink and deathtouch. Also, none of them are sorceries, which would have been slick with Quick Sliver...

­Homing Sliver / Sliver Overlord are probably the best Sliver cards to use with changeling instants. Prot-colour from Ward Sliver doesn't work, and I don't even think Ghostflame Sliver works - both of them want to only apply to permanents. Essence Sliver might work if there were any changeling burn spells, but there aren't... There aren't any "Whenever you cast a Sliver spell" triggers or even "Return target Sliver card from your graveyard" effects, so sadly it doesn't really have as much of an interaction as you'd like.

Yeah, I only realised when I saw Alex link to it here. And yes, I think Alex is correct that anything that says "Sliver" probably refers only to permanents (and would be errata'd to say so if necessary?), and only things that say "spells" include Sliver instants and sorceries.