id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
8512	Do not display discardable keys or warn if one is modified	stefanct	team	"Since theses tags on nodes/ways/relation are filtered on upload anyway there is no reason to even show them to the user on default.

Hence IMHO it would be best to not show it at all, maybe with an option to force its visibility. Another option would be to show them but inform the user that these changes will not be uploaded whenever he tries to modify/delete the tag.

If there is any doubt what I am talking about, it's created_by et al as defined by getDiscardableKeys():
http://josm.openstreetmap.de/browser/josm/trunk/src/org/openstreetmap/josm/data/osm/OsmPrimitive.java?rev=5754#L643"	enhancement	closed	normal	13.11	Core		fixed	created_by