There are many requests for "Copy comments to Split Stories" or "Copy Attachments to Split Stories".

It could be solved, instead, by elevating a Story (any Backlog Item / Defect / Test Set) to an Epic (Portfolio Item) when splitting, and maintaining the description, conversations, attacments on the Epic. The child Backlog Items would primarily be used to carry the tasks, and track Story Points, effort, To Do, whilst the communication / specification would be at the epic level.