Does rclone supports uploading only the part of a big file that has changed? I think it's supported in Backblaze B2 and Dropbox but I don't know if rclone, as a cliente of this services, has this feature and in what services.
No it doesn’t support modifying only part of a file. As as far as I know, none of the APIs for the cloud storage providers support binary diffs.
The link you posted was for the backblaze backup tool, not the B2 iterface. I imagine the backblaze backup tool uses something like the B2 API but uploads binary diffs as separate objects. This is hidden from the user as part of the program.
By the look of it dropbox do the same thing too: http://stackoverflow.com/questions/12758013/dropbox-differential-incremental-uploads-using-rest-api