Further to my original idea, may I propose that PTC enhances the 'Redefine' and/or 'Edit Definition' dialogues as follows:
In the RMB Menu accessed when I right-click a reference, add a 'Replace' option.
Then, when I either select the incorrect reference during the original creation of the feature, or when my feature fails regeneration because a reference has gone missing, I am able to replace that reference with the appropriate one.
As an extension, make the Edit Definition and/or Redefine dialogues maintain their settings, even when a reference is replaced. For example, imagine I define a datum plane which was defined as parallel to another plane and through an axis. Imagine that, at a later date, my axis goes missing and the datum plane fails. I enter the 'redefine' dialogue and right-click, 'Remove' the missing axis, preparatory to selecting another axis that does exist. Unfortunately, the first reference, the one that does work, and was left undisturbed, immediately changes to 'Through'. I then need to change that back to what it was to make the redefined feature work. This is even worse when redefining holes, when dimensional offsets become lost for ever unless one has the foresight to write them down first.