Are you suggesting I remove all changes except for the FileSource class?  I could then do the overloaded apply in my project since I don't know what optional parameters I might want @ the time.

If I left the change in scalding I would need an overloaded apply method for all the possible optional calls as well. The single boolean call would have to be left out since I wouldn't know which one the client code wanted to set. 

def apply(p: Path, fields: Fields,  sm: SinkMode): Tsv = 
def apply(p: Path, fields: Fields,  skipHeader : Boolean, writeHeader: Boolean, sm: SinkMode): Tsv = 
def apply(p: Path, skipHeader : Boolean, writeHeader: Boolean, sm: SinkMode): Tsv = 

Ideas?