To improve the usability of a revision history, change untangling, which reconstructs the history to ensure that changes in each commit belong to one intentional task, is important. Although there are several untangling approaches based on the clustering of fine-grained editing operations of source code, they often produce unsuitable result for a developer, and manual tailoring of the result is necessary. In this paper, we propose ChangeBeadsThreader (CBT), an interactive environment for splitting and merging change clusters to support the manual tailoring of untangled changes. CBT provides two features: 1) a two-dimensional space where fine-grained change history is visualized to help users find the clusters to be merged and 2) an augmented diff view that enables users to confirm the consistency of the changes in a specific cluster for finding those to be split. These features allow users to easily tailor automatically untangled changes.