Can you provide some examples of what you mean?
You can do something like
{ IF { REF somecondition } = "Y" "base form" "possesive form" }
e.g.
{ IF { REF somecondition } = "Y" "dog" "dog's" }
but you would need to do that for every word, or know all the
necessary rule to do e.g.
if it isn't "it", "he", "she", "we" and so on then if it's a singular
noun not ending in s then use noun's...and so on... and that's
assuming we're talking about modern English...
Peter Jamieson