Kaplan is Polish for priest. Kaploun is a variant.
Kogan is another variant of Kagan; it came about because of the lack of a hay sound in Russian. Sometimes it is followed by typical -ov and -sky type Russian endings.
Persian Cohanim are called Betaharon and Cohenzedek (Kohanzadegh) as well as Kohanian.
There are a couple of Bukharan Cohen families whose names have nothing to do with kehuna.
In Creedmoor, the Admou”r receives pidyon gelt for every baby born, bechor or otherwise, but his surname is Schmoigerman (Shoiteh, Menivel, veGas Ruach), hardly a sign of kehuna.