how has God changed? its people who do.
example, jesus never said to pray to mary or other saints. we, the believers are referred to as saints in the bible. but catholics have extra books called the Apocrypha...which origins are debated. google it for more info.
then jws came about when an 18yr old decided he didnt like parts of the bible and somehow came up with their beliefs. they have made many inaccurate prophecies. God shows himself to us through his prophecies, and he says when prophets say things that do not come about, then they are false prophets. prophet means teacher also.
then mormons...came from Joseph smith, which there are testimonies of neighbors and others who say he was a fraud and the golden book he had was really a false historical book written by a dead author, with added bible verses to it. one of the claims in the book is that jews came over to america, ohio is really the new kingdom, and native americans are descendants of jews. and their jesus is not even the same idea as other christians.
then there are doctrine debates about faith and works, rapture and so forth.
so, God's word never changed. its just that people try to change it.
