I hope I've gotten the terms right...
As you say, the lines are blurred. The literal disassembly"”and reassembly in a form that highlights aspects of garment construction"”is the most obvious type of deconstructionism. The Antwerp six and Rei Kawakubo's Comme des GarÃ§ons are good examples of this, although it would be a mistake to label them as merely "obvious." Armani is a "deconstructionist" in the figurative sense of one whose work displays a reconsideration of form and function, without the "unfinished" look of his more radical colleagues. To lump Armani and Kawakubo in the same category shows how unhelpful categories can be, since their philosophies are in many ways diametrically opposed. Armani's raison d'etre
is finding new but flattering ways to drape fabric on the natural human form. Kawakubo's interest in the human form is as a foundation for her sculptural clothing; she prefers to obscure much of the body's natural shape, revealing parts as an exercise in deconstructing anatomy through clothing. I don't think "modernism" is a separate category so much as a broader, inclusive one. It's not inventing new styles without referencing the old; referencing the past is unavoidable. Modernists, however, are looking for a fresh angle"”a reinterpretation of some sort. I don't think you can do that without some degree of deconstruction, but somone like Issey Miyake is a modernist for whom deconstruction is a mere preliminary to the real work. So, not all modernists are deconstructionists, even if all deconstructionists are modernists. The "classicists" (for lack of a better term) are primarily interested in refining pre-existing models: that's a Brioni or Kiton kind of philosophy. Ralph Lauren is a different kind of classicist; unlike the Italian classicists, Lauren likes to explore (and exploit) varying iconographies. Also unlike the Italians, Lauren has a broad populist streak; he makes his fantasies accessible to the masses. I don't think Slimane makes any fewer references to past styles, but"”ripped shirts aside"”he's not primarily a deconstructionist. He has the constricted color palette (black white and red) and severity of line of a minimalist, but he employs quirky details (bug-shaped crests, oddly looped belts, deliberate runs in his fabrics, esoteric shirt collars) in a way that, say, Calvin Klein would not. Despite his punk references, he's too elegant to be a real punk. He employs classic lines, but exaggerates their linearity in a non-classic way. So, we might call him a "modernist" without sticking him into any of the subcategories. OK, I'm hip-deep now. Maybe LA Guy can dig me out.