Can you use royal icing for buttercream?

[Megatron]

I've bought the wrong bloody icing for a birthday cake I'm about to make. Can I use royal or will it go weird? Could I just blitz up normal sugar to make powdered sugar and try that instead?

bekicookscakesblog.blogspot.com/2012/05/leftover-royal-icing-as-buttercream.html how to make it into buttercream. how to make powdered sugar (which you will need to make the buttercream) www.biggerbolderbaking.com/how-to-make-powdered-sugar/

It’s fine to use it for buttercream. But: get any lumps or clumps out of the sugar first! Lumpy bits don’t blend in in the same way as they do with normal icing sugar, as I found to my cost. I smoothed them out in the end, but it was a struggle.