I would just do it in a low key and unobtrusive fashion
If you've already been using it, and are now only going to hardcore it, then I can't see that it should make any difference to anyone. The planners only get alerted to changes if it's in an obvious position so they can't help but notice, or else if a neighbour complains. It doesn't sound as if that's likely in your case.
In addition, if you've been using your alternative entrance for more than 4 years without any action being taken by the council, then you have established a lawful right to carry on using it. (Look up CLEUD - certificate of lawful use or existing development.)