Awesome
tile-decorator 
A JavaScript module for decoding Mapbox vector tiles, doing various modifications in JS and reencoding back. It can:
- add new properties to a layer (
updateLayerProperties) - filter out features that don't have specific properties (
filterLayerByKeys) - select properties to keep on each feature (
selectLayerKeys) - merge features with the same properties and type into one, and sort geometries within one feature by proximity for better compression (
mergeLayer) - get all values of a specific property in a layer (
getLayerValues) - rename layers (
layer.name = 'foo') - rename keys (
layer.keys[2] = 'kittens')