I created a Herald rule visible to noone (a personal rule), and now I want it to be a public rule, but there's no way to change the visibility of it. Is this intentional?
The different rule types are more than just different visibilities -- they have different actions available, so they can't be changed without loss of information in the general case. For example, only personal rules can "Mark with Flag", and only global rules can "run build plans" or "require legal signatures".
The conditions are the same, so we could maybe let you "Create Similar Rule..." or something like that, to make it easier to build a global rule with the same conditions as a personal rule or vice versa.