Try the spray on some older leaves first. Generally, soaps are safe on powdered Echeveria leaves although sometimes they will leave a stain. You don't have many options really, those aphids have got to go.

Where there's aphids, there's usually ants, so try to get them too.

If the plant and pot are not too big, you can also submerge it into a bucket of water for a few minutes, the aphids will all die from suffocation.