It is not necessary to open the tin in advance; on the contrary, the opening is part of the ceremonial in front of your guests. To open the tin (which is vacuum-sealed), use a lever such as a key or a coin.
To maintain its freshness during tasting, place the caviar tin on a bed of crushed ice. If you don't have a caviar service set, place the ice in a small bowl or shallow plate. So caviar service sets do not require ice. Simply place them in the freezer a few hours before tasting.