Welcome to Just Answer and thanks for your question. I've been looking since you first posted your question. Is this the same John SIMPSON who married XXXXX XXXXX (1679-1747), daughter of XXXXX XXXXX about 1699 in Charles County, MD?
If so, he was the son of Thomas SIMPSON (1618-1690) and XXXXX XXXXXe WILLAN (abt 1622/3-1690) who were marriedXXXXX Mary's Co., MD. Thomas was from Stratherrick, Invernesshire, Scotland. He was christened 17 Nov 1618 in Newbattle, Midlothian, Scotland. Thomas was the son of John SIMSONE[sic] and Janet HOG.
His wife XXXXX XXXXXe WILLAN was born about 1623 in Warwick, Cumberland, England to Richard and Elizabeth WILLAN of Warwick.
Sic is Latin and just means that is the way it was spelled in the source I saw. Spelling wasn't that big a deal before the 1900s and things were often recorded the way they sound. You will find Simpson (and many other given and surnames) spelled many ways - Sympson/Sympsson/ etc. Phonetic spelling has resulted in names like "Szeine" being "Jennie." That is one of my favorites. It isn't really that a name "changed," it's just that is what it sounds like.
I found this excellent resources after I had answered you. It probably goes into far more detail than you want to know, but I'll pass along the link any way.