If there is one command called "Paste", and another command beginning with and commonly abbreviated to "Go", "Paste and Go" should be equivalent to using both in sequence. If it's impossible to make it act in the expected manner, and impossible to label it correctly, the only remaining option is to remove the feature.
most non-technical people treat urls mostly as blobs (which doesn't mean they don't understand it's consisted of parts, but that's irrelevant)
so the URL field is mostly operating one urls as a while
that's why if you click on it in difference to normal text it will always select the whole url, because most times most people will either copy that url or fully replace it
similar "Past and Go" also operates as the url as a whole, not text segments. So it pasts the new url to where the old url was and "goes" to the new website
additionally if you don't just replace an url but edit it a "do this edit and directly go without giving me a chance to double check it" functionality doesn't really have any reason to exist as its way too niche and people who do that likely anyway use keyboard shortkuts instead of the context menu
sure there probably could be a better name e.g. "Replace Tab and Go". Or they could not show it if you don't have all text selected.
But "Past and Go" isn't a description of functionality anymore but has become something like a slogan or special term. So neither renaming it nor changing behavior is really acceptable from a UX POV.
Technical people have the tendency to use keyboard shortcuts.