mine modem ip address is 10.20.30.40 but mine isp ip address is 182.57.xx.xx

so how to forward post from modem to get private ip address as identity

how to get modem ip address identity on network
i mean when some one sees mine ip address it should come 10.20.30.40 not 182.57.xx.xx

is there any software which can change ip address to 10.20.30.xx

i want to change ip address to range 10.20.30.XX .
like example mine machine should send signal that mine ip address is 10.20.30.xx
whether it is possible