Best position is based on the combination of skills a player has, and it is not something that is set in stone. Therefore, as players train and change skills, positions might change.
You shouldn't be doing your line-up without a clear idea why you put players into their spots, so a change like this shouldn't really matter.
"I don't know half of you half as well as I should like; and I like less than half of you half as well as you deserve."