Well, in most cases “correcting a fillet” means extracting the affected surfaces, untrimming them, deleting of some unnecessary geometry, adding new surfaces and fillets… The process is totally manual and time-consuming. I just did something similar to a model that needed some small modifications. Lots of mouse clicks and use of the best Rhino plug-in made by @jim that could be downloaded from the following link:
It’s a good practice to save numerous versions of each important model in a dedicated layer, so that it will be easier to use an earlier version as a base for the modified end model.