I do know how to change some of the settings of an existing threaded hole feature by code, but I have never done so with the help of an iLogic Form before. I have just done simple hard-coded size/thread changes from one specific size to another. The code process for making these changes is a bit more complicated than some other similar sounding tasks though. It might be a bit to complex to simply explain here by typing stuff in a forum post. An example file, and example Form, and example ilogic rule would probably be in order to more properly convey how this automation task could be set-up.
I do know that currently the only way to have a multi-value list in a simple iLogic Form is by using a multi-value parameter, which is rather limiting. And I also know that we can not make multi-value iProperties yet, which would be nice. If the iLogic Form is an 'internal' one (versus an 'global' one), then any changes you make within the form will immediately effect the model, without waiting for you to click something like an Apply or OK button, which is usually really nice, but that behavior can make it pretty difficult when you need to set multiple settings correctly before applying those settings to the model. For instance, if the model currently had a really small diameter threaded hole, and you were changing it to a much larger threaded hole, when you first select the other larger diameter in the form, it will immediately try to apply that to the model, before you can change the thread to one that would fit that size hole, so it might throw an error, or reject the parameter change, or break the feature. When using a 'global' iLogic Form, changes you make in the form must be applied by clicking the Apply button or OK button, before they will effect the model, which might be better in this case, but I have not tested it in this exact scenario before.
Wesley Crihfield

(Not an Autodesk Employee)