Martin (1992: 330):
As with the unpacking of grammatical metaphors discussed above, this procedure [lexical rendering] radically changes a text's mode. This makes it inappropriate for register analysis which attends to contextual dependency.
 Analytical procedures, such as lexical rendering or unpacking grammatical metaphor, do not change 'a text's mode'. The mode of the text depends on the context of its creation, which is distinct from the actions performed by a discourse analyst.
Halliday & Matthiessen (1999: 321):
… there is a third contextual variable that is specifically concerned with the part language is playing in any given context — the symbolic mode, how the linguistic resources are deployed. This covers both the medium (spoken, written, and various subtypes such as written in order to be spoken) and the rhetorical function — persuasive, didactic, informative, etc.
 Since neither lexical rendering nor unpacking grammatical metaphor can affect the mode of discourse, this is not a reason for excluding them for register analysis.
 The relation between register and context (i.e. situation type) is realisation. Analysing a register necessarily includes identifying the field, tenor and mode variables of the situation type that the register of language realises.