In winrar if you enable recovery record option it will modify rar file itself, it will make it bigger by 3-10%. It will not modify files contained inside it any way. (im not sure where exactly winrar stores recovery record, but guessing across the rar file itself)
Good thing the Syncrify is smart and will update your RAR file partially after you enable recovery record. 1000MB file will be synced by 100mb and make it bigger on server.
I would sugjest using 10% recovery record,