I do not know anything about Magyar / Hungarian grammar so can not give you an answer.I do know, that most of the ancsestors changed their surname. Are you getting this spelling from an American paperwork or ?? If you do locate a name of a village and order the church films you might encounter the ancestral names being spelled maybe three different ways.
The Slovak alphabet does not changes. An O is O and not an A.In Magyar: Csillag, in Slovak : C'illag but same pronounciation. At this time I would not worry about the name but locate a name of a village.