掮在背上 He Took The Tally And Flag
好大聖，只為師父阻路，沒奈何幹出這件事來。就把他牌兒解下，帶在自家腰裡，將「令」字旗掮在背上，腰間掛了鈴，手裡敲著梆子。好大圣，只为师父阻路，没奈何干出这件事来。就把他牌儿解下，带在自家腰里，将「令」字旗掮在背上，腰间挂了铃，手里敲着梆子。
逐句解 Line by line
Splendid Great Sage! It was only because his master's road was blocked that he had brought himself to do such a thing.
只為 keeps 為 as wèi, for the sake of — the other band of the character from the two wéi a passage earlier. The narrator is supplying the excuse Pilgrim did not quite make for himself.
So he undid the demon's tally and hung it at his own waist, shouldered the banner with Order on it, hung the bell at his belt and took the wooden clapper in his hand.
解下 keeps 解 as jiě, to untie — not the administrative jiè ruled far earlier in this chapter. Four items, taken one by one off a body, and 著 in 敲著 is zhe. The disguise is no longer a copy. It is the original equipment.
The narrator steps in to excuse the killing before Pilgrim has quite finished regretting it, which is a small and revealing intervention. The book would rather the reader had a reason.
Then the stripping of the body, itemised. Tally, banner, bell, clapper — the same four things the disguise was assembled from at a distance, now taken from the man himself.
It is a grimmer scene than the earlier transformation and the novel does not mark the difference. Pilgrim is not imitating a Little Borer of the Wind any more. He is wearing one.