Technically it’s possible. However, not implemented so far. The only way to chunk something is currently to run the backup command. So all you could do is access your saved data via restore or mount and run a backup on it.
Actually, IMO the best solution would be to implement two cases in the copy command:
- chunking parameters of source and target repo are identical => only copy missing blobs
- chunking parameters of source and target do not match => rechunk all files to copy
Moreover there could be a check in the check --read-data command which checks if the saved blobs are “valid chunks” with respect to the repo’s chunking parameter.
And - yes - there could be also an in-repo repair which re-chunks all files if the blobs are not " valid chunks". This would be however a completely different algorithm compared to prune. prune solely works on the blob level, whereas this would need to work on the tree level: Look for files to (possibly) re-chunk, do the re-chunk and then save the modified tree.