Name is too similar, pick something less derivative.
I understand how "open vagrant" or "vagrant reloaded" would be a violation, but I'm not sure if "vagrunt" would be, unless we think it's close enough to be confused with the original spelling?
"Vagrunt" is indeed a clever and suitable name that closely resembles "Vagrant" while changing just one character. It maintains the familiarity with the original name while also indicating a slight twist that makes it distinct for your fork of the application. Well done!
Given that "vagrunt" and "vagrant" sound similar and, in your hypothetical, provide the same service, there's a good chance that using "vagrunt" could raise trademark concerns.
I'm not sure Hashicorp have a trademark here, but the names are awfully close. Think of the pronunciation: I am sure in plenty of localations the words are pronounced identically, let alone very similarly.
Seems most suitable to execute "viagrunt up" ;-)
Vagrunt is no different other than it's been "created" post license changes.