Hey Louis- a lot of people have made that 1st suggestion quite a lot on this forum and we hope there'll be a future update that addresses that issue. It's annoying cause if you adjusted the beatgrid on your computer/laptop after exporting it to a hard drive, only way to add the updated version of the file is to delete it from the hard drive and re-add it.
as for the 2nd one, it would have to be the same feature in rekordbox that checks what files have been deleted & also knows what files have been updated- then it'll be able to re-add the file to the hard drive/SD card. The feature has been suggested before so let's hope it get's added :)