Sure. I don't think this clause means a damn thing. Suppose we agreed that Nato wanted to "conquer" Yugoslavia because it saw the country as an annoying residual of socialism and desired to expand the EU Empire (sic). "Serbia is a dagger pointed at the heart of Macedonia." The clause doesn't give them the legal right to do that. Obviously there could be no such legal right, and no agreement would contain any such option. It lets Nato troops rampage through the country "legally," but a takeover would still be way beyond the bounds of the agreement.
Second, there is no reason why Nato should want Serbia. The EU has plenty of better candidates to absorb, as the article Louis posted pointed out. That whole process is likely to be drawn out. What could possibly be the urgency of conquering Serbia? What industrial treasure awaits the EU? What spoils of war? The Yugo plant? If they want Serbia's industrial plant, why are they blowing it up, along with infrastructure needed for it to function?
Maybe all that Nato wanted was easy access to Kosova from outside. Maybe they wanted to be able to pursue Serbian paramilitary who committed terrorist acts in Kosova. Maybe the language was unduly provocative to the Serbs, maybe on purpose, maybe out of stupidity. What does it matter now? Nato sucks. We know that.
As a practical matter, if Nato wanted an agreement that permitted them to safeguard Kosova, it would need something like the clause. More important, since Nato is pretty much the only hope for Kosova, the clause would be necessary. If any settlement was likely, which seems increasingly doubtful.
Frustration with our present powerlessness seems to prompt us to consider what might have been, three weeks ago or three months ago. I don't think it matters too much to Kosovars. History matters, as WL said, but we can always discuss that at their leisure. Kosova is screwed, and I doubt that the East Timorese, Palestinians, or Kurds are any better off for it.