You can use the caret and the Scissors tool (key command U) to split notes at any point - so to turn a whole note into eighths, activate the caret at the start of the note, then select 8th notes (press 5) then press Space U Space U Space U etc to cut your way along the note.
(Edit: other users have also suggested a “copy rhythm” feature - is there a way to copy and paste a rhythm pattern, just the pattern? - that would apply just a rhythm pattern to existing notes, which (were it to exist) you could hypothetically use to a similar effect to your original post.)