Can we include a new Dwaraka Shila along with Salagrama Perumal-s to perform Tiruvaradhanam? Are there any stipulations to be followed like consecrating it, etc.?

One can certainly include the new Dwaraka Shila along with Salagrama Perumal-s to perform Tiruvaradhanam. During the first time, it is enough to perform Tiruvaradhanam with milk.