Gumroad: https://gum.co/sync_keys
What this addon does is, when you insert keyframes (globally) or move them around (Dopesheet / Graph Editor), transition keys (Breakdown / Extreme / Moving Hold) will automatically adjust relative to the original value.
By default, keyframe types have no functional purpose and are only used for visibility in the Dopesheet, so there’s no option to set them in the Graph Editor.
As such, I included a menu in the context menu (W / Right Click) to set the keyframe type in the Graph Editor, similar to the one in the Dopesheet