Fine-Tunning
Each marking was of course one of the prime letters that was changed ever so slightly by Baracus before being inscribed right into Hao Xuan's bones with the help of the nanites.
Once Hao Xuan broke into the Seventh Stage of the Spirit Realm, he realized that he was able to once again control the majority of his spiritual powers with a lot more efficiency.
And during one of the hundreds of Celestial Gateway experiments, one thing became clear. He didn't actually have to physically enter the celestial gateway anymore.
By placing the rune sequence within his body, he could send his consciousness into the gateway and in turn, move about with a lot more freedom than before since he wasn't restricted by his physical form anymore.
He was able to navigate the gateway using his own body and soul as a conduit, exponentially decreasing the time it would take to find the way back.