Here is a list of the changes to the Sunnah, the way of the Prophet, made by the rashidun Caliphs:

Abu Bakr

According to Sunnis

According to Shias

• Abrogated Ali's leadership.

• Stole the land of Fadak from Fatima and also usurped Muhammad's heritage from all his relatives.

• Abu Bakr payed the Prophets depts in spite of him telling that only Ali was allowed to do that

• Fought Muslims only because they didn't recognise his leadership and didn't want to give him Taxes.

Umar

According to Sunnis

• Changed the adhan

• Forbade the lamentation for dead relatives, including his daughter, in contrary to what the Prophet meant.

• Changed the number of floggings for drinking alkohol from 40 to 80 lashes.

• allowed people to "tripple divorce"

According to Shias

• All the above, and the following:

• Umar took the solitary prayer of the month of ramadhanand changed it to congretional prayer.

• Forbade temporary mariage

Uthman

According to Sunnis

• Forbade relaxation between Hajj and Umrah 1 2
• doubled the morning prayer

According to Shias

• -

Ali

• Restored all the above to the default.