In your examples, which is a relative pronoun. It introduces a relative clause. And in English, a relative clause has a gap, a missing element. Let's look at an example:
1. The box belongs to me.
This is a fairly simple sentence. The noun me is the object of the preposition to. Let's try turning that into a relative clause.
First, we replace me with a relative pronoun:
2. the box belongs to who
(In modern English, we'd usually use who, but in very formal speech whom would be more appropriate. More on that later.)
Next, we move the relative pronoun to the front of the clause, leaving behind a gap:
3. [ who the box belongs to ____ ]
Now we have a relative clause! We can use it as part of a larger sentence, if we like:
4a. I'm the one [ who the box belongs to ____ ] .
In this case, we can optionally replace the relative pronoun who with that:
4b. I'm the one [ that the box belongs to ____ ] .
And we can delete that from the sentence altogether:
4c. I'm the one [ Ø the box belongs to ____ ] .
Sentences 4a-c are all fine. You can use any of them! But if you wanted to make the sentence more formal, you'd want to make two changes. First, we'd replace who with whom:
5a. I'm the one [ whom the box belongs to ____ ] .
And second, we'd do something called pied-piping, in which we move the preposition to to the front of the relative clause:
5b. I'm the one [ to whom the box belongs __ ____ ] .
In formal style, this is the proper phrasing. (Note that this sentence is not more correct—it is merely more formal. It's important not to confuse correctness with formality.)
You can use any of sentences 4a, 4b, 4c, or 5b:
4a. I'm the one who the box belongs to.
4b. I'm the one that the box belongs to.
4c. I'm the one the box belongs to.
5b. I'm the one to whom the box belongs. (formal)
But, and this is important, you cannot duplicate the preposition to. All you can do is move it! That means your examples are incorrect. Compare the following:
6a. Identifies the site name [ to which the GL code belongs __ ____ ].
6b. *Identifies the site name [ to which the GL code belongs to __ ____ ].
In formal style, sentence 6a is perfectly correct. The relative pronoun which has been fronted (as it must be), and the preposition to has followed it to the front of the clause (as is appropriate in formal style).
But in 6b, you've come up with an extra preposition! Where would this preposition come from? Well, if we undo the pied-piping, this is what we get:
6c. *Identifies the site name [ which the GL code belongs to to ____ ].
It sounds pretty silly with to to there, doesn't it? Since 6c is ungrammatical, the derived sentence 6b is ungrammatical as well.
So no, you cannot use those redundant prepositions.
In this answer, the * symbol indicates that a sentence is ungrammatical in standard English.