If I'm in Safari then after right clicking on a link, the context menu will show "open link in new window" on top, and "open in new tab" below that.
Is it possible to swap them, or completely remove the "open link in new window"?
Generally in macOS you can't customise the order of items in menus.
For this, though, you could just avoid the menu entirely by Cmd ⌘ - or Cmd ⌘ Shift ⇧ -clicking the link, depending on how you have your prefs set.