Datapacks are unable to overwrite vanilla json files found in minecraft\worldgen\noise_settings.

It is possible to edit the vanilla dimensions which was recently solved issue here: MC-187904

,but if there is not much you want to change about a vanilla dimension, then you'll have to copy the entire code in the matching noise_settings .json file to the settings field in the dimension .json file, and edit it there, which is inconvenient.

In the file I attached to this issue, I edit the sea_level from 63 to 32.