Short answer: You can't. It may or may not brick your system but no one is going to want to be the guinea pig to find out. And obviously if you ever removed CBHC without removing the mod, that would be a guaranteed brick as it would fail to load the Wii U menu.
Long answer: CBHC or another CFW like Mocha could patch this all on the fly (it may be easier to do with Mocha as that does more on the fly patching than Haxchi CFW does, so the framework for patching files in titles on the fly might already be there) so it wouldn't require actually modifying the NAND. But seeing as the Wii U is dead and all the homebrew devs have long since moved on there is not much chance of that happening.