That is called an "Ossia", it is a musical term for "alternatively". Which means the player can either play the alternative passage or the original passage. The Ossia is frequently used in Liszt's pieces. The Urtext for Balakirev's Islamey also contains many alternative passages.
Here is an example of an Ossia notation in Liszt's Hungarian Rhapsody No.6 in Db Major.
An Ossia passage could sometimes be notated only for one clef like in the example. Although I'm not sure if you could change the use of the sustain pedal in the alternative passage, it's better to ask a professional or a teacher. Or someone who might know.