I'm afraid i've got rather lost in this thread.
 As an after thought after seeing other posts on the issue, I think  more  than  a  generic  warning  that "may  break  the  image"  the  Monticello comments and/or a  simple explanation on the reasons and  affected  packages *before*  the update  starts with  an  option to  proceed or abort is much in need.
 Yes, maybe.  Then thing  is that I  am not  sure in which  cases it would break. Only  in overrides? How many overrides  do we have from external pacakges in Core stuff?  I have no idea.
I think given that we are at a very early stage of building the Pharo image from PharoCore i.e Metacello just coming on etc, we should simplify the concerns above. Basically we should only build Pharo on top of a known PharoCore. Just because packages don't contain overrides does not imply that moving the core image will break packages on top. Don't offer such a feature, and then worry about what will happen. Part of the Pharo build script should set a flag that prevents system update in the short term. Longer term we should switch the available update mechanism to #loadLatest on the ConfigurationOfPharo. There is then one System update feature, but different implementation in Pharo vs PharoCore. cheers, Mike