You can land a mahseer in winter too. there is no hard and fast rule. The best time to try in winter is when the sun is up and shining brightly. Try pools insted of rapids.
Give it a try and you may get lucky.
Yes true as long as they are hungry they go for any thing that seems/smell like natural food. Just take care that you mimic injured fish action while playing with Spoon.
Example the place I go for Mahaseer hunting on River bed there are many silver gold threaded cloth peice which we Hindu release after pooja or worship in the river. Mighty Mahaseer still go for the Silver color but only when you resemble your action like injured or live fish.