||We describe research on understanding group mutability in the behaviour of external groups, and how interventions by coalition forces may affect the behaviour in terms of controlling hostile groups and encouraging friendly groups. We explore how emotion may influence the behaviour of individuals by affecting the type of reasoning that they undertake, encouraging uncritical rather than critical thinking. We describe a computational framework holding a cognitive model of an individual operating within a group context, inspired by theories from social science. Individuals relate to in-groups and out-groups and have beliefs that are associated with emotions. Cognitive Appraisal Theory is used to evaluate incoming memes pronounced by external speakers, appraising the effects of the memes on an individuals self-esteem taking account of their group relationships as indicated by social identity theory, and leading to an emotion in the individual. Appraisal is followed by a process of coping that seeks to handle the effects by either performing problem-focussed (critical) or emotion-focussed (uncritical) thinking, according to the current emotional state of the individual. This model is implemented within a Cognitive Architecture (Soar) as a set of reasoning processes that handle beliefs and emotion. The model is integrated into a multi-agent simulation tool (Repast Simphony) allowing the simulation of populations of individuals interacting and spreading rumours, or memes, together with interventions. We describe how this framework could be used to construct experiments to explore how different situations lead to group mutability and behaviour, together with the effects of interventions by coalition forces.