First off, replace Lapras and Jynx. While you might say Lapras is a very important part of this team, it really isn't that great. Seeing how your foe has three turns to stay in on Perish Song, they can easily take down Lapras in that time. Jynx COULD use Mean Look, but Jynx is too easily taken down. Perish Song just isn't that effective. Replace them with two important members of a Hail team, two Pokemon that no Hail team should be without: Glaceon and Walrein. I would also replace Cloyster with the superior Regice.
Mamoswine: I would replace Blizzard with Ice Shard. Mamoswine has an amazing attack stat, and priority is always important.
Regice: Blizzard, Thunderbolt, Focus Blast, Explosion (works great with Froslass)
Abomasnow: Replace Grasswhistle with Leech Seed and give it Substitute. Combined Leech Seed and Hail can easily rack up damage, and Substitute protects it from all those weaknesses.
Froslass: Give it Spikes, Froslass has now replaced Cloyster and allowed you to use the much better Regice. Blizzard is a must of course. Thunderbolt offers nice coverage. Shadow Ball is another obvious.
Walrein: Considered the second most important on a Hail team (after Abomasnow of course.) Give it Leftovers and combined with Ice Body, Substitute, and Protect, it has been known to stall the foe for 32 turns. Surf and Blizzard allow it to easily go on the offensive.
Glaceon: The heavy hitter on the team. Blizzard off of that high Special Attack? Yes please. Shadow Ball and HP Fighting give it nice coverage, and Wish is good for team support.