Upgrading Items to Legendary with Umbral Shards

Latest PTR update reduces the Gear Score required for using Depleted Umbral Shard from 600, to 590. This also introduces a side effect, which allows you to convert some items from Epic to Legendary.

Those are items that come with a preset perks list (mostly named items), where you lose the last perk unless it is 600 Gear Score, such items are: Infamy, Will of the Ancients, Beginning, Featherweight Ring, Doom's Chance Earring just to name a few. Upgrading these kind of items to 600 Gear Score using Umbral Shards, will unlock the fifth perk slot (fifth? read technical explanation below), making them Legendary.

We've also got an Umbral Shards Guide which contains a list of all shard requirements and reward values.

Technical Explanation

Lets start with some basics - items can have up to 5 perks (not 3). From a technical point of view, attributes and gems (or gem slots) are just perks. The maximum amount of perks an item can have is decided by the item's Tier and Gear Score. A Tier 5 item needs 600 Gear Score for it to be able to have the last perk slot unlocked (which is needed for legendary items).

The Gear Score - Perk Count system is used in two different ways:

1. When dropping/crafting/obtaining in any way, an item with random perks, you will only roll for the eligible perk buckets, based on the item's Gear Score (which is rolled before the perks).
2. When items have a preset list of perks, the system is still used to "disable" non eligible perks. This is what happens to, for example, Infamy when it is below 600 Gear Score.

Case #2 is what we're interested in. Even if the Gear Score is too low for the last perk, the perk itself is still attached to the item, compared to case #1 where it isn't. The perk gets disabled. If you use Umbral Shards to bump up the item's Gear Score too 600, it will unlock the last perk slot (which already has a predefined perk inside), and the item becomes Legendary.

This case applies to every single item in the game which has a preset perk list, where the last perk just gets disabled due to low Gear Score.

There's also some fixed gear score items, like Guillotine, which can also be upgraded to legendary. AGS is probably gonna remove the last perk on these - they already did that with Needler, which no longer has Refreshing Move on PTR.

What remains to be seen is if this is intended, or just a slight oversight. I personally hope it's intended, or if it isn't, that it stays, since it makes it more enjoyable knowing your 599 Gear Score Infamy isn't gonna go to waste.

Edit: Kay from AGS has confirmed on the official Discord server that this mechanic is intended.