You can add two Nuget deployments, one target Nuget, another Myget (Nuget deployment with Server URL specific to Myget). Then use conditional deployment to setup which branch deploy to which deployment.
Regarding -pre prefix is it about file name? As I understand .nupkg files are being created with build.ps1 script, so you can use APPVEYOR_REPO_BRANCHenvironment variable in script to rename .nupkg files when needed, e.g. add -pre prefix when APPVEYOR_REPO_BRANCH equal development.
Hope I understood your questions correctly. If not, please elaborate.