alt Hacker Newscmd+shift+r in goland, push to a branch, open a PR, ask devops to make the old location archived and prevent further writes. After a couple months remove access to the old one and see what breaks.
You know, normal development task, small amount of story points..
You're now arguing that it's easy, which is a completely different argument. The comment I responded to argued that it's unnecessary ("just do the rewrite in go.mod, leave source files unchanged").
For my thoughts about why it's not easy, see this comment: https://news.ycombinator.com/item?id=49870363