AoS starter Sigmarines are mono-pose models with fixed weapons, but they're, well, weapons. You can just cut off the hammer on both sides of his hands, drill a hole, put a pin in it and then glue sword/whatever pieces over it.

With good plastic glue you can even skip gap filling if you were precise enough, because those glues melt plastic, so if there's tiny gap, it'll close on it's own.
Will be harder with the shields, you can't really convert those hands as they're fused with the shield, but they're still cut off at the elbow, so little converting and you can put weapon arms in there easily!