It is sometimes possible to treat an improvised weapon as a real weapon of a similar shape (the PHB giving the example of a table leg being used as a club). Now, let's say you take a real weapon, and want to use it in the fashion of another weapon (gaining the other weapon's traits).
Example 1: you have a whip and a bag of rocks, and you want to use them as an improvised sling.
Example 2 : you have a blowgun, and you want to smack people with it just like you would do with a quarterstaff.
My question is : Can you do that (use a weapon as an improvised version of another weapon, provided that it makes sense) ?