I can mount my Live Ubuntu partition with this
sudo mount -o remount,rw /cdrom what i'm asking is simple.How to make that command running automatically on every Live USB boot ?
Place that command in a script and add the script to the init scripts. If you are using some init-alternative, place your new script where appropriate or follow what ever structure it may use for storing commands that will be executed on run-time.
If you want to know how to add scripts to init, look at this thread - How to install an init.d script in ubuntu?