WTPart creation is typically governed by access control rules. If you don't want users to create parts, don't grant them privileges to create parts. ACL's are created/managed in the Policy Administrator. You could create a rule at the ORG level that includes an absolute Deny to part creation.
Do you want to limit it to creating new parts or want total system denial? For migration, I would place the whole system offline to any access. This can be done by changing the IP address or blocking the access to the system at your routers.