Changing word inflections

This might be an unusual question. I have a situation where I am creating paraphrases with a rule based system. One transformation that I’d like to implement would one that gets rid of light verbs, like so:

a) Steven made an unwilling concession to us.

b) Steven unwillingly conceded to us.

To go from (a) to (b) requires some inflectional changes such as:

unwilling -> unwillingly

concession -> conceded

Is there something out there that can take care of such inflectional changes reliably for a given word? Seems like there should be, but I don’t recall seeing anything like this.