Is there a way to rerun an Upgrade Step in Plone?
Go to portal_setup (from ZMI), then:

go in the "Upgrades" tab
select your profile (the one where you defined the metadata.xml)

From here you commonly can run upgrade step not yet ran. In your case click on the "Show" button of "Show old upgrades".
I've got a Plone 4.2.4 application and from time to time I need to create an Upgrade Step.
So, I register it in the configure.zcml, create the function to invoke and increase the profile version number in the metadata.xml file.
However, it might happen that something goes not really as expected during the upgrade process and one would like to rerun the Upgrade with the corrected Upgrade Step.
Is there a way to rerun the Upgrade Step or do I always need to increase the version and create new Upgrade Step to fix the previous one?