Answer
You need to manually copy the contents of the generated .cre file into a corresponding .cdb file, maintained per component per customization. Once that .cdb file itself is created, it does get automatically picked up and added to install.tem on its own. This manual step exists specifically so changes can be tracked and managed as distinct CDB files within the current track, and later graduated into UPG (upgrade) files when moving to the next track, rather than the .cre content being deployed directly and untracked.