Pleasant first appears on the 1840 Lawrence County, Mississippi census as a head of household. He would be about 21/22 years of age. He is listed there with his wife, and two male children less then 5 years of age. This is an accurate portrayal of Pleasant and Jane's family at the time:
Pleasant, Jane, C., and Jasper N. I have not yet identified the full name of the male child C., as he is listed in 1850 as only C., and not residing in the house by 1860. It was common practice in this 1850 census for families to identify given names only with initials.Pleasant then appears on the 1850 census as Pleasant Blanton. The indices online are correct in the spelling of the name as it appears on the census. Without a doubt, Pleasant's family was identified as Blanton, instead of Bryant, by the enumerator. Was this an accidental mispelling, or a deliberate name change? I believe because he was enumerated properly in 1840, that this was the enumerator's mistake in spelling the name from the pronounciation given at the time. This is not the only surname consistently mispelled by this enumerator.
Further credence to the mistake being made in the spelling is that Pleasant was enumerated in 1860 in Columbia, Marion County, Mississippi, as Pleasant Bryant.
So when you are searching the census records, you may often come across widely mispelled names... while this may portend that your ancestor switched names, more often then not, it is only the case of bad spelling.