Is it possible to set up dynamic priority for files, so if some file has been added to synced folder but other files are being transferred at this moment - I can tell Resilio to start syncing this recently added file?
Unfortunately, you can't set up priority for files to transfer.
Starting from Connect 2.3 there is new job priority feature. But that applies only for newly created jobs. This article describes this new feature in detail: https://connect.resilio.com/hc/en-us/articles/360000006084-Job-priority