Please find the answers to your question as follows:
Q1) Yes, it is possible.
Call the API "CyU3PUsbForceFullSpeed ( CyTrue);" before the CyU3PConnectState (CyTrue, CyFalse); API
(The first API will force the device into full speed. The second API will enable USB 2.0 connection. If the first API is not called, the it will be a high speed USB 2.0 connection instead of a full speed USB 2.0 connection)
Q2) No, only 64 is allowed. Other values are not allowed by most OS.
Hope this help!