Yes, the Sabbath has legitimately changed, because there are modern conveniences today that allow people to do more leisure activities on the Sabbath. The Bible simply says to do no work on the Sabbath. The Bible is silent on whether it is acceptable to participate in leisure activities on the Sabbath. Although religious ceremonies are still important, the Sabbath can now include travel and family activities.
Let's take the bible as our basis, in Exodus 20:11 says,
"wherefore the Lord blessed the sabbath day, and hallowed it."
In this text, we see how God has valued the sabbath, to the extent that he makes it holy.
Ezekiel 20:12 says, "I gave them my Sabbaths, to be a sign between me and them, that they might know that I am the Lord that sanctifies them."
God has established his Sabbath for two things: first, to commemorate his creation, second for it its also a sign between him and us. (Exodus 31:13, Ezekiel 20:12)
Im ain't started yet, I just layed out the foundation.
There is none in the bible account that God said he transferred his Sabbath to the 1st day, which is Sunday. God has repeated his Sabbath, that we should observe it, over and over again from the Old down to the New Testament.
There is only one religion who freely admit that they had changed the Sabbath. Which they still claim that no scriptural text could support their claim.
"The Pope has power to change times to abrogate laws and to dispense with all things, even the precepts of Christ"
- Decretal De Translat. Espiscop. Cap
"...Perhaps the boldest thing, the most revolutionary change the church ever did happened in the first century. The holy day, the Sabbath, was changed from Saturday to Sunday... Not from any directions noted in the scriptures."
- Saint Catherine Catholic Church Sentinel, May 21, 1995
Deuteronomy 4:2 says,
"Do not add to what I command you and do not subtract from it, but keep the commands of the LORD your God that I give you."
I guess they're subtracting the Sabbath to the True Commandment.
So I hope I answered your question. Therefore I conclude that Sabbath has not legitimately technically, if we claim that the bible is only our creed..
No, the Sabbath day has not legitimately changed, because it still means the same religious celebration that it has always meant. The way that people celebrate the Sabbath has changed, because the way people enjoy relaxing and recreation has changed. But the Sabbath is still the same day to worship God and relax that it has been for centuries.