Martin (1992: 136-7):
Grammar also plays a rôle in transforming the identity of a participant. The Attributes referred to above as not themselves realising participants are commonly used to add qualities to and/or classify a participant in a new way. The Attribute in [3:72] serves both functions:
[3:72] The woman went off to visit her step-sister, who was an old potter who lived in the woods.
Attributes extend the ways in which a participant can be identified; the grandmother can be referred to as the potter, the old lady, the older woman and so on as well as her step-sister in the text following [3:72].
Material processes are also commonly involved in transforming participants. Renovation of this kind is exemplified in Halliday and Hasan's (1976: 2) example, reproduced as [3:73] below. Obviously the process of washing and coring apples transforms their identity, and the participant presumed by them is not experientially identical to that referred to with six cooking apples; this would be even more radically the case had the recipe suggested wash and chop instead of wash and core.
[3:73] Wash and core six cooking apples.
Put them into a fireproof dish.
 This confuses the instantial identity of a participant with the cohesive resource for referring to elements in discourse —the system of reference. This confusion undermines the model in this chapter because it makes it inconsistent with its purported aim: 'reference as semantic choice'.
 In the realm of the ideational metafunction, the outcome of 'transformative' material processes is an elaboration, extension or enhancement of the Actor (‘intransitive’) or Goal (‘transitive’) (Halliday & Matthiessen 2004: 186).
 To be clear, what the Halliday and Hasan example demonstrates is the anaphoric personal co-reference made by the pronoun them.