Exclude Lambda function from deploy to a particular stage

You can put those definitions on a different property and use variables in order to choose which definitions to use.

environment-functions:
  prod:
    some-prod-function:
      handler: prodFunction.handler
      events:
        - http:
            path: /prod-function
            method: post
  dev:
    some-dev-function:
      handler: devFunction.handler
      events:
        - http:
            path: /dev-function
            method: post


functions: ${self:environment-functions.${opt:stage}}      

You may need to change this depending on how you specify your stage on deployment (${opt:stage} or ${env:stage}).