How can I preserve a Jungle that was generated with Corruption inside it?

In my world, the Jungle was generated with multiple large veins of Corruption running right down the center of it, as well as throughout the Underground Jungle. I'm interested in preserving as much of my Jungle as possible as I transition into Hardmode, and would like to take whatever steps I can to help protect it beforehand. I know that I can create an artificial Jungle if needed, but I'm playing on a large world so I'd like to preserve the large naturally-occurring Jungle that I already have, if possible.

I know that it's possible to "inoculate" an Underground Jungle in early Hardmode by deliberately spreading Hallow around it before the Corruption has a chance to reach it, since Corruption can't overwrite Hallow. However, I am unsure whether that technique is applicable since the Corruption already exists inside my Jungle. I also know that it's possible (though laborious) to un-corrupt land that has been taken over by the Corruption, but I'd greatly prefer to prevent the Corruption from spreading any further, rather than having to do damage control afterwards. The existence of the Corruption that's already there doesn't bother me, either, I just don't want it to get any worse.

Are there any simple steps I can take (pre-Hardmode) to ensure that my Jungle isn't fully taken over by the Corruption once Hardmode starts? (Preferably ones that involve less effort than manually excising the interloping Corruption block-by-block. :))

In order to save your Jungle, you need to act quickly to contain it completely. Dig a gap that is at least four blocks wide surrounding the entire corruption. Note - on the bottom side, Corruption will send down hanging vines that will spread corruption, so you must also line the bottom with a non-corruptible material like Wood.

If it's not feasible to contain all the corruption this way, the best you can do is isolate some parts of the Jungle and Underground Jungle with a four-block wide border, so you have at least some jungle to work with until you get a Clentaminator and enough Green to cleanse the corruption - which will allow the Jungle to spread to those tiles again.

If you dig a 4 block wide empty space around the entire corruption, then it shouldn't be able to spread any further