Your example sans thief is answered on page 34: “Not all mythoi are opposed to the shedding of blood. Indeed, some require their priests to use swords, spears, or other specific weapons. A war deity might allow his priests to fight with spears or swords.”
It then gives a list of suggested deities (by “mythoi”, by which they mean things like “death”, “hunt” and so on).
In stock AD&D 2e, there is no multi-class cleric/thief. However, there are other cleric combinations, and “Regardless of his other classes, a multi-classed priest must abide by the weapon restrictions of his mythos. Thus, a fighter/cleric can use only bludgeoning weapons (but he uses the warrior combat value).” (p. 45)
So it isn’t also being a thief that would alter a cleric’s weapon choices, but their deity.
Dual-class is more restrictive, but the basic rule is that “the character must still abide by the restrictions of whichever class he is using at the moment.” The example is, almost fortuitously, a cleric who changes to fighter, but the example does not mention weapon choice.