Question first:
Are there 5e precedents outside the DMG for differences in players identifying the capabilities of Artifacts as opposed to other magical items? This could be a rule in a sourcebook, a specific item in an adventure, or anything else.
Background:
Artifacts are a type of magic item, and as the DMG says "Each artifact has its own magical properties, as other magic items do…." There is no specific text in the DMG on how the properties of artifacts are identified, but we know that in general magic items can be identified using the Identify spell or by focusing on the item throughout a short rest.
While there doesn't seem to be any specifics about Artifacts in general being identified differently from magic items, the DM is given more latitude with Artifacts "for they are as much plot devices as magic items".
Some sample Artifacts also have additional, if unclear, guidance on the extra steps needed to access some of their capabilities (though not to identify those capabilities). For example, the Book of Exalted Deeds has (emphasis mine):
Once you’ve read and studied the book, any spell slot you expend to cast a cleric or paladin spell counts as a spell slot of one level higher.
The Book of Vile Darkness has (emphasis mine):
A creature attuned to the book must spend 80 hours reading and studying it to digest its contents and reap its benefits.
Some other items also have additional requirements to access their powers.
Best Answer
Identification isn't activation.
I think you're mixing up two different things here. Identifying an artifact works just like any item. You cast the spell or spend the time, and you find out what the item is, what it does, and how it works.
Now the "how it works" might include attunement, a command word, or spending 80 hours in study. But that's not part of identification, that's a usage requirement. Spending time to read and digest a book is like putting on a suit of magic armor, just a lot slower.
The DM might decide that a particular artifact is immune to identify and have some alternate way of determining its abilities, like making friends with the intelligence that lives in it, but that's entirely the realm of DM fiat at that point. Going purely by the basic rules, artifacts identify just as readily as anything else.