When i update a song (with review needed, for example adding short edits etc) it will display again in the new music tab as a new upload?
Yes, it will appear as a new item on dashboard page.
no, it will not display as a new upload/published item because that item already published and you done an update. you will be bale to see your update item in the ‘Newest’ tab but may be not in the first page because it will show publish date ascending order. So, if your item published many days ago then it will place accordingly (publish date ascending order).
for update item no. there will only show newest published items.