It is likely that those values are driven values rather than driving values.
It is the hole tables that can be edited. If the value is not there then there is no default.
What you might be able to do with relations is drive the drill depth based on thread depth. I found this to be a shortcoming in the software since quite often, shops have a standard rule for how deep the drilled hole has to be for a given full thread tap depth (plus tap taper). Of course, then you also have bottom tap options which throws in a whole new column of data. I suppose by the same token, you can drive the thread depth by relations based on the either the major diameter or the pitch. I prefer relations such as this to be driven at the feature relation level, the hole feature in this case. But this does make it an additional operation when the hole is created. Maybe a UDF is called for here to make sure it is all managed consistently.