You can change the bandwidth dynamically in the prototype cake scheduler,
but you can't change it to be bandwidth unlimited.And it is not clear how
much damage it does a live system to change it.

root@ranger:~/git# tc -s qdisc show dev eth0
qdisc cake2 803c: root refcnt 9 bandwidth 20Mbit precedence flows
 Sent 2384 bytes 9 pkt (dropped 0, overlimits 1 requeues 0)
 backlog 0b 0p requeues 0
          Class 0   Class 1   Class 2   Class 3   Class 4   Class 5   Class 6   Class 7
  rate      20Mbit 17500Kbit 15312Kbit 13398Kbit 11723Kbit 10258Kbit  8975Kbit  7853Kbit
  target     6.2ms     6.2ms     6.2ms     6.2ms     6.2ms     6.2ms     6.2ms     6.2ms
  delay        0us       0us       0us       0us       0us       0us       0us       0us
  maxpkt         0         0         0         0         0         0         0         0
  pkts           3         0         0         0         0         0         6         0
  bytes        482         0         0         0         0         0      1902         0
  drops          0         0         0         0         0         0         0         0
  marks          0         0         0         0         0         0         0         0
root@ranger:~/git# tc qdisc change dev eth0 root cake2 bandwidth 5mbit
root@ranger:~/git# tc -s qdisc show dev eth0
qdisc cake2 803c: root refcnt 9 bandwidth 5Mbit precedence flows
 Sent 6604 bytes 22 pkt (dropped 0, overlimits 2 requeues 0)
 backlog 0b 0p requeues 0
          Class 0   Class 1   Class 2   Class 3   Class 4   Class 5   Class 6   Class 7
  rate       5Mbit  4375Kbit  3828Kbit  3349Kbit  2930Kbit  2564Kbit  2243Kbit  1963Kbit
  target     6.2ms     6.2ms     6.2ms     6.2ms     6.2ms     6.2ms     6.2ms     6.2ms
  delay        0us       0us       0us       0us       0us       0us       0us       0us
  maxpkt         0         0         0         0         0         0         0         0
  pkts           3         0         0         0         0         0        19         0
  bytes        482         0         0         0         0         0      6122         0
  drops          0         0         0         0         0         0         0         0
  marks          0         0         0         0         0         0         0         0

root@ranger:~/git# tc qdisc change dev eth0 root cake2 bandwidth 100mbit
root@ranger:~/git# tc qdisc change dev eth0 root cake2
root@ranger:~/git# tc -s qdisc show dev eth0
qdisc cake2 803c: root refcnt 9 bandwidth 100Mbit precedence flows
 Sent 23830 bytes 83 pkt (dropped 0, overlimits 4 requeues 0)
 backlog 0b 0p requeues 0
          Class 0   Class 1   Class 2   Class 3   Class 4   Class 5   Class 6   Class 7
  rate     100Mbit 87500Kbit 76562Kbit 66992Kbit 58618Kbit 51290Kbit 44879Kbit 39269Kbit
  target     6.2ms     6.2ms     6.2ms     6.2ms     6.2ms     6.2ms     6.2ms     6.2ms
  delay        0us       0us       0us       0us       0us       0us       0us       0us
  maxpkt         0         0         0         0         0         0         0         0
  pkts           3         0         0         0         0         0        80         0
  bytes        482         0         0         0         0         0     23348         0
  drops          0         0         0         0         0         0         0         0
  marks          0         0         0         0         0         0         0         0