D for %s never means anything else than 1:00 saving.
Within the current tz database, sure, that is presently the case. But this is not necessarily the case within ACTUAL practice; "D" could conceivably be used to refer to a DST offset of any amount, since it is still "daylight saving time", just of a different amount.
I am not making the argument here that the terminology is used this way in Australia/Lord_Howe; only that if it is, then LHDT is a perfectly suitable (and indeed, preferred) abbreviation for UTC+10:30+0:30 as observed there in the summer. To be clear, I haven't seen any evidence either way, but I don't particularly believe any residents of Lord Howe Island would call it "Lord Howe half-daylight time", because to them, half an hour is a full transition.
Granted, this has not always been the case (see four summers from 1981–1982 to 1984–1985), but I suspect residents understood it as a change to "daylight saving time" itself, while still referring to it in the same way. Whatever the case, we should reflect the terminology in use, and not aim for anything more.
I have not been part of this project for very long, but I believe most of the "invented" abbreviations have been simply to fulfill POSIX requirements where no commonly-used English terminology previously existed. In the case of Australia/Lord_Howe, one would presume that such terminology already exists, so we should use that, whatever it is.