Vim: Replacing a line with another one yanked before

Vp: select line, paste what was yanked

What I would do :

1. 36G (replace 36 with the line number you want to go to)
2. Y
3. 70G (replace 70 with the line number you want to go to)
4. Vp

You don't have to leave normal mode, but it does yank the line. You can however use V"0p which will always put the line yanked in step 2.