One major controversy in the study of code-switching (CS) has been the treatment of structural regularities or patterns. Formal approaches attribute these patterns to syntactic constraints or models that are independent of socio-pragmatic or discourse factors, and hence they fall short of accounting for the variation and diachrony of CS constructions. Functional approaches call for due consideration of inter- and intra-speaker variation and discourse or processing factors, but they do not seem to go very far in pinpointing precisely what factors motivate a particular structural pattern. This paper attempts to integrate these two approaches in examining an emergent pattern in Cantonese–English CS in which postmodifying phrases are attested with English prepositions. The form of the construction may well be captured by some version of the Null Theory, but nonetheless it has little to say about why it is a new and variant pattern in Cantonese–English CS. This paper suggests that the construction is prompted by discourse factors such as salience, information status (i.e. given versus new) and heaviness (of the modifying noun phrase); typological differences (i.e. word order difference between Cantonese and English) and syntactic properties of words (such as prepositions) also have a role to play. Diachronically, this paper suggests that the construction evolves from a continuous English noun phrase with a further switch, which this paper terms “reinsertion”, within this noun phrase. Variants and possible changes of this postmodifier construction are also discussed in the light of “reinsertion” and “schematization”.