Once you purchase a premium outfit, that outfit will be saved to your account. However, in order to wear it again, that same outfit first needs to be one of the offered options. If it is, you will be able to wear it again for free.
Also, if you decide to re-read a story, all the outfits you purchased while reading it for the first time, will be free.
Also, if you decide to re-read a story, all the outfits you purchased while reading it for the first time, will be free.