Hi @nfelixCXUGM. Sorry, but the short answer is no. This same exact thing has been asked for many, many times before, but it still has not been implemented yet. You can search for this idea in the Inventor Ideas forum and vote for it if you want, but no guarantees about when or if it will happen. Right now, we can only have a multi-value UserParameter. We can also make lists within our iLogic rules, then show a dialog with the list in it, to have a user select one (or more) items in the list that way. But an iProperty can only hold one value right now.
Wesley Crihfield
(Not an Autodesk Employee)