Tectonically_Neglected is dead on with this advice. Most of the good stuff in Zermatt in the winter is non-glaciated or in the case of Stockhorn, technically a glaciar but not a big worry since it's receded so much.
In Chamonix the crevass danger seems managable above 3000m because all the rain that's fallen was snow up there, so I would imagine Schwarztor, Breithorn, etc. are also fine although I suspect few people will start making tracks there until mid-March due to the "you will die without a guide" culture there.
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