This seems really neat. I have a question that I hope isn't something I'm missing, but is there an easy way to change the rendering ruleset? I ask because I've been wanting to build some custom maps for mountain bike trails in the state where I live and have them served up similarly.

Whenever I've looked into other projects for this it's either focused on rendering tiles from Mapbox data (where not all the OSM tags -- especially not MTBing ones -- are available) or really old info or presumes that someone else will be generating tiles.