Modify Imported Content

I am wanting to modify the data on my tile server. I have a brief idea that I can do something with an api, however I have no clue about how to get it all working. Any pointers would be appreciated!

Hey Niklas,
Modifying the data you have already imported may not be a straightforward task, but you could generate a new data in a .osm file and merge it with your existing database using osm2pgsql