Many people say that some things are impossible to do via magic, like flying, growing new body parts, or even just changing the colour of your eyes.
However, is the point of magic not to do the impossible?
I'm not saying that all spells work. They need to be well-composed, and well thought out. Otherwise, the spell will fail. Using items in spells makes them better.
If, however, you find a good spell, and you're full of energy and belief, any spell can work for you. (Well, any spell idea. If the spell is badly written, it might not work.)
So, don't give up on 'impossible' spells yet. Really, it's hard to tell where magic ends and impossible begins. Most people think no magic is possible, but it is. Why would it be any different for this?
No witch is a god/dess. They can't call down lightning with a thought. They can't snap their fingers and turn somebody into a toad. That is what I think is 'impossible' or 'fluffy'. The thought of instant 'microwave magic'. Just dump this and this into a pot of this and stir it up while saying this, and bam, you're a fairy. Drop a mushroom on the ground while hoping really hard and lightning will strike the mushroom.
That is not how magic works.
Magic takes time. More intense spells take more time. And it's a good idea to try some simple luck or money spells before moving on to bigger works.
But don't give up on your dreams because people say it's physically impossible. If a deity is capable of doing it, you are capable of appealing to them. The universe works in mysterious ways.
(And if you really can't do it, the astral plane is always there! It can not only allow you to test your fantasies, but create a 'blueprint' for making them real. Look up 'shifting'.)