So, too, Pale Horse will rise from the ground
It will break its fast on the first part of us
It will consume us whole

I'd say there is no such way. I first assumed Purification (Watcher's Valeren) would work with it, but it does not.

That's a secret you want to hide till your Second Death in VtM, even if the aura marks that indicate it usually fade in 5 years, the fact you've done it still remains.

Well, I would say that OP's question is valid. Take Deviant trait for example. It is also not exactly something to be proud of, depending on the Path. It is also reputational trait gained by something one did in the past. And one can't simply say "Okay, I've been totally vanilla for 3 days 14 hours 37 minutes, I am no longer deviant".

And yet, the Purification removes deviant trait easily. Even though from purely technical perspective cleansing an aura should be much easier than altering the memories of all the unfortunate witnesses of one's sexual adventuries with that ghouled bunny.

Even if your aura has been cleansed, you have still Diablerized someon. A big no no in most Vamp Paths. So you still have that secret that you don't want leading you to your second death.

Annoying that we can't get rid of it. Definately. i've tried a few Diablerie heavy runs and just praying my intrigue and my spymaster's intrigue are enough to hide it.

But the fact that it lingers is lore appropriate.

I find this the hardest part of the mod, Create new name or web of knives is your best friend in this scenario. Unfortunately, some of the vampire disciplines make it near impossible to hide your secrets, so this will happen eventually. Maybe make sure you have a counter discipline before devouring vampire souls perhaps. The right disciplines are way more effective than having high intrigue.

Some vampires start with this secret like Dracula and have a good chance of it getting revealed. Best option then is converting to a Sabbat religion. Which kind of fits lore wise for Dracula, for his early days at least.

I feel like having the Diablerist trait should give a dread modifier as well as negative option. Which would make this a much more viable although still challenging play-style. Could even have Diablerist tiers giving higher negative option but with higher dread as well.

By the way, in the first edition of the latest changelog there was a line about possibility of getting rid of diablerist trait if you repent hard enough. It now appears to be edited out, but I remembers.

I would be cool with idea of diablerist trait giving dread if only dread itself was not purely positive stat as it is right now. It's just too easy to be both feared and loved. Dread giving additional opinion penalty would be too harsh, but giving proportional deduction to personal scheme powers sounds about right with -100% at 100 dread. Of course there are many bonuses to compensate for that, and scheme power would never be a zero really, but it needs to be carefully balanced at least in the start of the game instead of collecting as much dread as possible.