The blockhead recited his spell, gave his head a shake or two, and cried: "Change!"

念動咒語 is setting the spell going; 搖了幾搖, a shake or two of the head. Then 變 — change! — and the method is exactly Wukong's, which makes what happens next funnier.

Sure enough his head came over changed, and looked for all the world like the little girl's face — only his belly stayed fat and gross, ungainly and all wrong.

真個 is "sure enough," the narrator sounding briefly hopeful. The head comes over; the belly does not. 郎伉 (láng kàng) is lumbering, ungainly, badly put together. A little girl's face on a fat pig's body, and the text does not spare him: 不像, not the likeness at all. 女孩兒 takes 兒 as ér.

Pilgrim laughed: "Change again."

再變變: go again. Wukong is laughing.

Eight Rules said: "Beat me if you like, then — it will not come over. What is to be done?"

憑你打了罷 — hit me if you like, then — takes 罷 as ba. 變不過來, it will not come over; 奈何, what is anyone to do? He has stopped resisting and started sulking.

Pilgrim said: "You surely don't mean a maidservant's head on a monk's body?

莫成 is "surely you don't mean" — an incredulous opener. 丫頭 is a girl servant, the word coming from the two-tuft hairstyle such girls wore, so it is literally "little forks." A maidservant's head on a monk's body: Wukong describes the result with the precision of a man enjoying himself.

To have made yourself neither man nor woman like this — how will that serve?

不男不女 — neither man nor woman — is still current Chinese for anything that has come out neither one thing nor the other. Here it is being used about a half-finished pig. 弄的這等 has 的 standing in for 得, the link to how a thing turned out.

Set out the Dipper-stance and hold it."

佈起罡來: take up the 罡 stance. 罡 (gāng) is the handle-stars of the Big Dipper, and treading the 罡 means pacing out the Dipper's pattern on the ground — a Daoist ritual step that puts the adept in the right alignment to work. Wukong is telling Bajie to stand still and hold the posture while somebody else does the magic, which is more or less the story of their partnership.

Then he blew a breath of immortal air upon him, and at once, sure enough, the body came over changed, exactly like that child's.

仙氣 is the breath of an immortal, and one puff of it finishes what Bajie could not. The transfer of power is done in half a sentence and never remarked on. 那孩兒 takes 那 as nà and 兒 as ér.

Then he directed them: "You two elders, take your households in with your son and your daughter, and do not get them mixed up.

寶眷 is "your honoured family," the polite word for another man's womenfolk and household. 令郎、令愛: your son, your daughter. 不要錯了 — don't get them mixed up — is a practical instruction and a very strange one to have to give. 教 is jiào.

In a little while, should my brother and I shirk and play sly and come walking in, it will be the harder to tell us apart.

一會家 is "presently, in a little while," 家 here just rounding the phrase off. 躲懶討乖 — dodge the work and play clever — is Wukong being disarming about his own side. 轉難識認 takes 轉 as zhuǎn, "all the more": once four identical children are wandering about, nobody will be able to sort them out.

Give them good fruit to eat, and do not let them cry out, lest the Great King get wind of it in the moment and the secret leak.

The instruction that gives the game away as a game: keep them fed with good fruit and keep them quiet. 走了風汛 is letting the wind out — the vernacular for a secret escaping, and the god in question travels as a scented wind, which makes the phrase sharper than it looks. 將 is jiāng; 教 is jiào.

Wait while we two go and have our sport."

耍子 is playing, larking about. It is what Wukong calls going out to meet something that eats children, and he calls every demon-fight in the book by the same word.