But it sounds like they are all in the Author (Year) format already, and the Original Poster wants them to be conventional (author, year)? But not sure why they would be already the alternate format.
If that is the case, though, then the unformated citations will look like this {Greaves, 2000 #5209@@author-year} and you can do a simple search and replace to find @@author-year and replace with nothing.
If as an alternative, the OP wants them to be author, year with no parentheses, they will need to edit the citation template to removed the parentheses altogether - but this will apply to everything cited (apart from one specified to use the Author (Year) template.