Is it possible to repent from teaching others how to access blocked websites that were used to enter pornographic websites?

Yes, repentance is possible and accepted, no matter how great the sins and transgressions, provided that the conditions for its acceptance are met and it occurs before the death rattle. Allah accepts the repentance of His servant and replaces his evil deeds with good ones, as stated in His Almighty قول: "Say, 'O My servants who have transgressed against themselves [by sinning], do not despair of the mercy of Allah. Indeed, Allah forgives all sins. Indeed, it is He who is the Forgiving, the Merciful.'" And His saying: "The acceptance of repentance by Allah is only for those who do evil out of ignorance and then repent soon after. It is those to whom Allah will turn in forgiveness, and Allah is ever Knowing and Wise." As for the people whom you encouraged to sin, you must advise them, guide them, and instill in them fear of Allah, to the best of your ability.