Thanks, wintonian, for the explanation of the clue, one of many that struck me as almost too abstruse to be justified (the 'musical piece' was another such).
As for the original artwork, the asymmetry is confined to the absolute extremities; there's nothing to suggest that the poor chap has suffered the displacement of an entire thematic item.
Alanw - the two clues you mention are further examples of over-egging.
For 'Priest ...', a single letter has to replace a two-letter abbreviation ('mask' = 'conceal by superimposition'); for 'Rum's', think where that island is and how its inhabitants say 'all', then add a one-letter and a two-letter abbreviation. Both clues lack a letter in their wordplay.