You need to use the -o option to modprobe in order to give the module a different name. The you given it is arbitrary and just needs to be unique.
# modprobe dummy ; ifconfig dummy0 up
# modprobe -o dummy1 dummy ; ifconfig dummy1 up
# modprobe -o dummy3 dummy ; ifconfig dummy3 up
dummy3: unknown interface: No such device
# ifconfig dummy2 up
# modprobe -o foobar dummy ; ifconfig dummy3 up
# ifconfig | grep dummy
dummy0 Link encap:Ethernet HWaddr EA:2A:12:AE:C3:A3
dummy1 Link encap:Ethernet HWaddr 96:3E:2B:F2:39:AC
dummy2 Link encap:Ethernet HWaddr EA:BD:69:9F:54:8F
dummy3 Link encap:Ethernet HWaddr EA:DD:D2:DE:F2:54
# lsmod | grep -E '(dummy|foobar)'
foobar 3400 0
dummy3 3400 0
dummy1 3400 0
dummy 3400 0