Is it possible to create a new in-text citation template within a style? I use the two that are built-in, but would like to add onto that list.
Those two are the only options. You can alter them. What are you hoping to get? Or you can modify the citation afterwards, right click in the formated citation and choose, edit citation, omit the author, or omit the year, and going to More… and adding text before it or after it, which makes it pretty adaptable.
two examples:
If you wanted “(see review Smith et al, 2012 for additional information)” you would put the addition text in the prefix and suffix (with the needed spaces after selecting more… option)
or “As shown by Smith and his colleagues (YEAR), the …” (omit the author, and type the text you want in the document itself).