There have been several suggestions made to improve the wikitree name search engine. However, pending software changes to do that -
The wikitree guidance for the Proper First Name, Preferred Name and Nickname fields:
may provide some help. Note that the Proper First Name field is intended to be a documented name, including the possibility that the name was officially changed during their lifetime.
I appreciate your desire to help others find the profile, but the wikitree guidelines should take preference.
Additionally, give the google search engine a few days to pick up your changes, and then try googling "wikitree kobas willemssen" That may provide an alternate means to help others find alternate spellings.