Import an updated GitHub repository without breaking a modified/outdated version of it in vendor directory

Question

Previously, a GitHub repository is got inside vendor/github.com directory, actually ~/go/src/myapp/vendor/github.com. It is modified and imported in some packages. So, it is both outdated and modified.

Now, in some other packages, I need to import and use the original GitHub repository i.e. updated and unmodified. How can I do that? What are my options? Any hint is appreciated.