On desktop, you can edit the link page previews: Page preview - Obsidian Help
There is a feature request to make embedded notes editable: Edit transcluded (embedded) notes (blocks) in place (likely requires WYSWYG first) - #187 by mattmaiorana.
I believe not. You could add the link before splitting the note, which would let you use multiple cursors to place a cursor in each section and type the link once. Or you could copy-paste the link into each section before splitting.