It's hard to specify a really long *Nodes option
Scott Bennett was quite confused by this (see this thread for details, http://archives.seul.org/or/talk/Sep-2010/msg00023.html ).
In theory we could change the ROUTERSET config type to be one of the types that you can only append to, not replace by setting another entry later on.
I'm not sure we should change this for 0.2.2.x, first because we are in feature freeze and second because this changes behaviour that someone might rely upon (setting the option via controller for example, expecting this to overwrite, not append to the previously specified entry). For this reason I'm not sure that's a good idea at all; now with Tor warning about this kind of configuration setup we should at least confuse fewer users about thinking that they can use more than one line to specify *Nodes.