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Description: Recent intervention research has shown that personality traits can be modified through psychological interventions. However, it is unclear whether reported effects represent changes in the trait domain or only some facets or items. Using data (N = 1,523) from a recent intervention trial (Stieger et al., 2021) the present study examined the effects of a digital-coaching intervention on self- and observer-reported personality facets and items. We focused on participants who wanted to decrease in Negative Emotionality, increase in Conscientiousness, increase in Extraversion, increase in Open-mindedness, and decrease in Agreeableness. We used measurement invariance testing to examine which level of the trait domain hierarchy changed during the intervention. For the observer-reports, the effects could be explained as changes in the trait domain. For the self-reports, we found some heterogeneity in the effects on Extraversion and Conscientiousness. Most notably, changes were strongest for sociability (Extraversion), productiveness and organization (Conscientiousness) facet. At the facet level, only the responsibility facet showed differential change at the item level. Overall, this suggests that the broad intervention approach managed to affect the trait domain level, with only some exceptions. We discuss the relevance of measurement invariance testing and measurement approaches for personality intervention research.