The multi-level perspective (MLP) theorises technological change as a process of niche innovations competing with incumbent socio-technical regimes. As a mid-range theoretical framework, the MLP invites complementary, more detailed theorisation of salient issues, especially the roles of socio-political agency in changing regime rules around technological competition. Taking a socio-cognitive perspective, this paper links the MLP with social representations theory, to show how a new technology is diversely 'anchored' in a familiar one for different agendas. The case study is a specific niche innovation - thermal treatments of municipal solid waste (MSW) within the UK's wider regime of energy-from-waste (EfW). Through landscape-level changes, controversy over incinerators has destabilised the EfW regime's rules. This instability has opened up opportunities for gasifiers as a niche innovation, yet gasifiers have also become an extra focus for conflict over incinerators' wider role in the waste hierarchy. Agents compare thermal-treatment options for MSW according to various criteria which have unstable, changing rules. These express different socio-cognitive frameworks, analysed here as diverse social representations of novelty. The case study offers an insiders' perspective on endogenous enactment, i.e. the conflicting roles of socio-political agency in shaping transition pathways.