It is impossible to alter files uploaded via BackBlaze as it creates the exact copy of the file on your computer. However, if you want to rename or remove any files or folders, there is a workaround when using CloudMounter. All you need is to download files/folders on your computer, make necessary changes and after that upload them to Backblaze again.
Note: In CloudMounter there is a restriction when dealing with large files or folders. If the file/folder is larger than 10MB or the folder contains more than 10 files you will receive the error saying that there was an error while renaming or removing files.