[mothered]

does this mean that I can take it to the courier's offices and it won't compromise success?

That Is correct.

As for how to close or seal the package, what would be the most appropriate way to do it? Because I suppose I have to make it look like it was tampered with, as I understand it?

That's how boxing Is designed to work.

I suggest you fully familiarize yourself with the method prior to applying It.