Is there a way how to make DO always reuse a tab if it shows the same path of where I am navigating to (regardless of the means of navigation or whether the tab is locked or similar issues)?
Unless, of course I have a specified modifier key pressed down (like alt e.g.).
That depends how strictly you mean "always".
If we're only talking about double-clicking folders in the file display, or clicking them in the folder tree, then it's probably fairly simple. (Folders double-clicked from outside of Opus should be covered automatically as well, I think.)
Also depends a bit on the scope you want it to search for reuse. Just the active file display? The dual file display as well? Other separate top-level windows as well? They are all possible, but some slightly more complex than others.
But if we're also talking about clicking things on the breadcrumbs bar, or random commands that run the Go command as part of custom operations, then it may become complex, and I don't think there is an existing command or script that can be adapted (although there are some which could be used as starting points). While just the tree and/or file display probably don't need scripting at all, making it work everywhere would most likely require a script add-in which uses the OnBeforeFolderChange event to cancel the navigation and activate another window and/or tab if it finds a match.