I'd prefer a way to discard eggs that are 2km or 5km (so I can collect higher level 10km ones, for rarer pokemon). But since that is not possible currently, is there a way to identify the quality of an egg before collecting it from the pokestop?
There is infact no way to even reject an egg, at a Pokestop.
Once the egg drops, you can not tell its distance without picking it up.
That said, of the egg drops, and you do not pick it up, the egg will still be added to your inventory. The same happens with any item that drops from a Pokestop.
Nope, the items you get from a Pokestop are random assuming you're not at max capacity of that item.