costing for arbitrary set of edges

Thanks for the great work on Valhalla. I've been using it with @pblack1C, and our use case is that we want to compare routing results with different factor/penalty costs on an arbitrary set of edges. We have tried using `avoid_locations` but the large number of `avoid_locations` that we are using is causing Valhalla to be slow.

There are two possible solutions to explore and we hope to get advice from the community/see if others are facing the same issue before starting on either:
(1) Pass in costing options for arbitrary set of edges, similar to what has been implemented for automobile costing (but only for specific type of edges like highway) and the arbitrary set of ids that can be used for inclusion or exclusion for transit. It's been mentioned in #1496 that `node_filter` or `edge_filter` is a possible way of doing this. We would ideally like a non-binary way of costing as well (i.e. not just exclusion/inclusion).
(2) Edit the .pbf tiles that Valhalla uses to create routeable tiles each time we have a set of edges that we want to apply different costing on. We have yet to look into detail about the tile building steps that Valhalla takes, and are concerned that this individual cost of tile building may take too much time.