I did notice the sudden use of the name Peder Pedersen “Lund”. But it’s found only in the 1850 census and the two death records in 1851 and 1852 – all within a two year timeframe and only in Knudsker Parish. And the children didn’t use it.
One possible explanation is that it was a temporary kind of nickname used to distinguish between several Peder Pedersens in the same local area. That “tradition” was quite common, and the nickname would often refer to the name of a farm or a local place name. A “Lund” is a “Grove” in English.
Peder Pedersen’s father didn’t use the name Lund, but I haven’t checked further back.