I'm also researching the surname Dyke in Bilston, Staffordshire.
Although I haven't come across the change from Dyke to Dykes between generations, I often see changes in census returns e.g. the same family could be Dyke in the 1841 census, are listed as Dykes in the 1851 census and listed as Dyke again in the 1861 census!
I also have the name Millard in my family tree, which is derived from Millward (the "w" being dropped in the mid 1840's). I have also have the name Flavel in which can have numerous spellings (Flavel, Flavell, Flavil, Flavill etc).