Not every leak and leaker is the same. If a tool/procedure like that existed, it would probably be used on people who could generate positive public perception of their actions.

Apparently the "vault 7" leak was centered around how devices were hacked to spy on private citizens and consumers. The public has a soft spot for people who leak things that expose direct invasions of privacy. Chelsea Manning on the other hand leaked documents that I don't believe would influence public opinion of them very easily (diplomatic cables and different military things).

If you were going to break the law (planting evidence) to smear the character of someone, smear the person who has a higher chance of the public siding with.

then why wouldn't they have used it against Edward Snowden? he revealed a whole mass surveillance operation, along with misconduct by NSA agents, and there was a lot of popular support for him.

I still agree they could have smeared him, but I don't think it's improbable that the porn was actually his. Pedophiles are skilled at opsec, keeping secrets and doing unsavory things, so their background suits working in IC if they can conceal their behavior. And if discovered by a foreign intelligence agency, they'd be easy to extort into spying.

Vault 7 released a fair bit of code, didn't it? It would benefit state adversaries to leak that publicly, by burning exploits the CIA's using.

How would it work with Snowden? "Yknow the guy who flew to Hong Kong and stated he deleted all his data? Turns out he still had one computer he forgot that just so happens to be jam packed with illegal porn."

Much easier to trap him in Russia and claim he's a foreign agent.

Because that dirty tricks team was busy with Assange

It was; they got the word "rape" printed next to Assange's name in hundreds of headlines despite the women involved saying that they were railroaded by police and that no rape occurred.

Character assassination is a common tool in the CIA toolbox.

Her court martialing could already happen without anything else needed, and was enough to get her up to 90 years in prison, of which she got a 35 year sentence.