USB CDC Receiving
yes you can but you have to modify the cdc base class code
the usb transaction is is setup in
USBD_CDC_ReceivePacket
...
USBD_LL_PrepareReceive(pdev,
CDC_OUT_EP,
hcdc->RxBuffer,
CDC_DATA_FS_OUT_PACKET_SIZE);
}
CDC_DATA_FS_OUT_PACKET_SIZE is 64 that tell usb layer to get ready to receive up to 64 byte from host.
you could set this to any 64 mulmiple if to receie more at once
But if you do it is likley to brake any default host “com driver” and s/w.
With that you’ll be abble to receive longer “usb transfer” but you want get any “64” byte long message 
on usb when both host and device side want to to do biger transfer than the max packet size (64 here)
it require both side to be aware of it so that a spcial zero length packet is send for any exact 64 byte transfer. without it the over side wait for more.
So it may work but with custom host s/w only.
;){kind=link}