It seems that the vagaries of name spellings have been driving Irish genealogists nuts for a very long time, so step forward Robert E Matheson, Registrar General of Ireland over 100 years ago in 1901 to bring a bit of order to everything! I came across his book fully entitled “Varieties and Synonymes of Surnames and Christian Names in Ireland for the guidance of Registration Officers and the Public in searching the indexes of Births, Deaths and Marriages” freely searchable and downloadable on archive.org – find it at https://archive.org/details/varietiessynonym00math.
I can’t claim to have read it cover to cover but there does seem to be an alphabetical list of variants that might help inspire you to vary your search strings and wildcards if you’re struggling to find someone. I must admit though I found myself pleasantly diverted by all the local examples of variants reported from around the country that he has documented in the opening chapters – some of them are just hilarious … see page 28 … Nappy for Penelope?! Gobinet for Abigail?! Seriously though, there are some good examples that make you think as the equivalents are radically different words.