Did Christ open the Door of Hell after he preached the Gospel in the realm of the dead?
The short answer is no.
History sees the work of evil (Satan and his satellites) throughout salvation history and into our modern times. How could Christ has already closed it? Satan runs somewhat freely from the times of Genesis until now. The demons have seemingly always been coming and going. They nevertheless remain condemned to hell.
The demons not in hell, still take their hell with them. The subject of hell is one not clearly understood. Hell could be a state or an actual physical location. We simply do not know everything. Fr. Gabriele Amorth, one of the most famous exorcists in the Catholic Church, in his book An Exorcist Tells His Story, that at the point of liberation of the possessed condemn the possessor to the Foot of the Cross. He make note that most exorcists condemn then to hell from where they come.
CCC635 Christ went down into the depths of death so that "the dead will hear the voice of the Son of God, and those who hear will live". Jesus, "the Author of life", by dying destroyed "him who has the power of death, that is, the devil, and delivered all those who through fear of death were subject to lifelong bondage. Henceforth the risen Christ holds "the keys of Death and Hades", so that "at the name of Jesus every knee should bow, in heaven and under the earth."
Now if Christ descended to the dead, it was so those in purgatory may be freed and live.
We can see a slight problem with the translation of the Latin word infernum. The English translation could be any of the following: the lower regions, Hades, Hell, underground and so on. As we see it is quite ambiguous so say the least. The word infernum in Catholic thought and tradition simply means the limbo of the just or as some say the Patriarchs or the Fathers. Christ opened the doors of limbo, but the souls bound in hell remain there to this day.
We can simply take a look at the Apostles' Creed. First in Latin:
Credo in Deum Patrem omnipotentem, Creatorem caeli et terrae,
et in Iesum Christum, Filium Eius unicum, Dominum nostrum,
qui conceptus est de Spiritu Sancto, natus ex Maria Virgine,
passus sub Pontio Pilato, crucifixus, mortuus, et sepultus,
descendit ad inferos, tertia die resurrexit a mortuis,
ascendit ad caelos, sedet ad dexteram Dei Patris omnipotentis,
inde venturus est iudicare vivos et mortuos.
Credo in Spiritum Sanctum,
sanctam Ecclesiam catholicam, sanctorum communionem,
To show where I am going allow me to post two English translations that interpret the word infernum differently.
I believe in God, the Father almighty,
creator of heaven and earth.
I believe in Jesus Christ, his only Son, our Lord.
He was conceived by the power of the Holy Spirit
and born of the virgin Mary.
He suffered under Pontius Pilate,
was crucified, died, and was buried.
He descended to the dead.
On the third day he rose again.
He ascended into heaven,
and is seated at the right hand of the Father.
He will come again to judge the living and the dead.
I believe in the Holy Spirit,
the holy catholic Church,
the communion of the saints,
the forgiveness of sins,
the resurrection of the body,
and the life everlasting. Amen.
I believe in God the Father Almighty,
Maker of heaven and earth:
And in Jesus Christ his only Son our Lord,
Who was conceived by the Holy Ghost,
Born of the Virgin Mary,
Suffered under Pontius Pilate,
Was crucified, dead, and buried:
He descended into hell;
The third day he rose again from the dead;
He ascended into heaven,
And sitteth on the right hand of God the Father Almighty;
From thence he shall come to judge the quick and the dead.
It goes against tradition to state that Christ descended to the hell of the damned and the damned comprises both the demons and the evil souls of individuals condemned through their sins committed while on earth.
Seeing that you make point of referencing Revelation 20:1-6. Here it is:
20 And I saw an angel come down from heaven, having the key of the bottomless pit and a great chain in his hand.
2 And he laid hold on the dragon, that old serpent, which is the Devil, and Satan, and bound him a thousand years,
3 And cast him into the bottomless pit, and shut him up, and set a seal upon him, that he should deceive the nations no more, till the thousand years should be fulfilled: and after that he must be loosed a little season.
4 And I saw thrones, and they sat upon them, and judgment was given unto them: and I saw the souls of them that were beheaded for the witness of Jesus, and for the word of God, and which had not worshipped the beast, neither his image, neither had received his mark upon their foreheads, or in their hands; and they lived and reigned with Christ a thousand years.
5 But the rest of the dead lived not again until the thousand years were finished. This is the first resurrection.
6 Blessed and holy is he that hath part in the first resurrection: on such the second death hath no power, but they shall be priests of God and of Christ, and shall reign with him a thousand years.
The Book or Revelation or the Apocalypse of St. John is a book containing various visions and revelations that have yet to be interpreted by the Church’s in a definitive manner. It generally deals with future events and the end times. In the end, the Gates of Hell will be closed for good and forever. How to truly interpret this passage, only time will tell. The future is not ours to see.
The Apostle’s Creed – an older and shorter Creed – uses the words: “he descended to hell.” It is imperative to remember that “hell, in this context, is not the place of the damned. Instead, it refers to Sheol. Because “hell” was deemed as a deprivation of God, this word was used correctly here but only in that context – not in the sense that the souls were eternally separated from God. - Christ in Limbo
Christ in Limbo
636 By the expression "He descended into hell", the Apostles' Creed confesses that Jesus did really die and through his death for us conquered death and the devil "who has the power of death" (Heb 2:14). - Catechism of the Catholic Church.
For more information seeing the following article(s):
Whether our atmosphere is the demons' place of punishment?
According to Catholicism, it it possible for Satan and/or his satellites to roam the earth, while still being in hell?