Is it possible to run geth for ropsten and mainnet in a same server if I changed all the port for Ropsten node trying not to conflict the ports used in mainnet?
geth --rpcport 8546 --port 30301 --testnet (for Ropsten) and geth (for mainnet)?
Yes you can. You must use different
rpcport if you want to do this, just as you suggested.
geth --port 30303 --rpc --rpcport 8545 ... geth --testnet --port 30304 --rpc --rpcport 8546....
rpcport in the first command are not necessary, as they are the default values. I have included them in order to be explicit.