You probably know by the lack of response that no one has experimented using charcoal. The most its been used is to put a layer of it on the bottom of a terrarium to keep the water collected from getting too stale.

There was a grower in Wisconsin that experimented fire burning on his pots of Sarracenia x moorie but I have been unable to locate his website.

Some growers use charcoal as part of their Nep soil mix. So some people say it works but others like Barry Rice, author of "Growing Carnivorous Plants" advices not to. In his experience it seems Nep's roots avoid growing and spreading to where charcoal is present.

So maybe you can experiment yourself using charcoal and post your results.

Sorry I don't have anything else to add.

Good luck.

The best I've used is Biogize-SD which is available on Amazon under 'soil detox'. They have an easy mix and apply bottle which I just run through my hose-end-sprayer. But they also sell it in bulk (40lb box). I'm convinced my tomato plants were suffering from herbicides big-time until I treated them with the AC. They revived nicely.

If your soil is the problem, CHANGE IT! Why add something that will just modify the problem when a total change will resolve the problem and the plant and go on growing i=without interruption.
Most Nepenthes grow in media that may be organic or even limestone based. Charcoal would be best for those subject to fires and burning which should recover quickly from ash build up.
The use of coco peat/bark is good but this breaks down too rapidly that they will require a soil amendment. I recommend the use of pumice when using coco peat products and also orchid fine to medium bark.
But as they break down, amend it by adding a media with these components to give it good air circulation.