Rename tag with existed tag name

[dinya]

For example, I have tags "RoR" and "Ruby on Rails".

I wanna rename "RoR" to "Ruby on Rails", but http://SERVER/settings/plugin/redmine_tags?tab=manage_tags raises Name has already been taken while I expect the redmine_tags will rename "RoR" for all objects used ones (in other words, it will replace "RoR" tag object with "Ruby on Rails" tag object).