This study examines nominal derivational affixes in a multilingual practice in the Philippines involving Hokkien, Tagalog, and English called Lánnang-uè. A feature of this practice is the systematic combination of affixes and roots (henceforth, 'system'). Certain morphological combinations (e.g. Tagalog prefixes + English root) are used frequently and are regarded by Lánnang-uè users as well-formed, while others are not. This paper seeks to examine the spread, stability, and possible patterns of sociolinguistically-conditioned variation involving this system in the Lánnang-uè-speaking community. I conducted an acceptability judgment experiment involving 65 users in Manila and found high rates of spread and stability within my sample. Factors such as age, sex, and attitudes towards mixing selectively conditioned how some speakers adhered to system. For example, older users tended not to follow the affix source language, length, and position condition of the system whereas male users only tended not to follow the first condition. Based on the findings, I argue that the derivational affixation system exhibits conventionalisation, and that it emerged due to identity negotiation practices led by younger and female users. I also argue that conscious positive attitudes towards mixing help shape the stable development of multilingual practices.