Identifying Vs Attributive Mode [Diagnostic: Reversibility]

Halliday & Matthiessen (2014: 278):

These [‘identifying’] clauses are reversible. All verbs except the neutral be and the phased become, remain (and those with following prepositions like as in act as) have passive forms … Clauses with be reverse without change in the form of the verb and without marking the non-Subject participant …