Yes.
I gave the Scarabs in the desert dangerclass of 9 so that they'd drop boss amounts of loot and to make them able of dropping Legendaries in the first place, gave Magisil 20000 weidghtedprob and put ZRareExpectation15 to 500 or so, which combined with Enhanced Perception made it so that every Scarab kill would roll a tier 15 item.
Result was only Magisil whenever a Legendary item dropped.
For my personal use, I manually edited the weightedprob of all tier 15 and 14 items to be much, much higher than those of tier 13 (most sets and legendaries) to ensure that when the game rolls ZRareExpectation14 or 15, it actually gives me an item of that rarity. The game rolling 15 only means that it can generate up to rarity tier 15, not that it will drop. It still determines the item to drop by the weightedprob, So even if you score ZRareExpectation15 but there is 1 Legendary and 15 normal uniques with the same weightedprob in the drop list, you still have only 1/16 chance of getting the Legendary.
I can give you my modded drop.txt if you want to see. In game, I noticed quite a bump in the drop rates of rarity tiers 14 and 15 without touching the ZRareExpectation.