GloVe = {{1, 2}, {3, 4}, {0, 0}};

net = NetChain[{
   EmbeddingLayer["Weights" -> GloVe],
   LongShortTermMemoryLayer[10],
   SequenceLastLayer[],
   2,
   SoftmaxLayer[]
   },
  "Input" -> NetEncoder[{"Tokens", {"a", "b"}}],
  "Output" -> NetDecoder[{"Class", {0, 1}}]
  ]

data = {"a a" -> 0, "b b" -> 1, "a b" -> 0, "b a" -> 1, "a b c" -> 0};

netT = NetTrain[net, data]

NetExtract[netT, {1, "Weights"}]

netT = NetTrain[net, data, LearningRateMultipliers -> {1 -> 0, _ -> 1}]

NetExtract[netT, {1, "Weights"}]