Change stream size limit workaround

I see there is an open ticket for the 16MB limitation on change stream https://jira.mongodb.org/browse/SERVER-55062

Until it is fixed, given a document can be 16MB as well, change stream can crash when we request the pre-image. Looking at https://www.mongodb.com/docs/manual/changeStreams/#change-streams-with-document-pre--and-post-images, it suggests to

Limit the document size to 8 megabytes

I wonder how can we achieve that with transactions, where we don’t know the full document size until the commit time.