How change a file on a read only partition? topic

I have a file where is defined the 'menu boot' for example:

Quote:

---

label live
menu label ^Try Ubuntu without installing
kernel /casper/vmlinuz
append file=/preseed/ubuntu.seed boot=casper initrd=/casper/initrd.lz quiet splash --

---

But it is into a read only partition, i can't mount (remount) it with read/write privileges

How can i edit that?
I need to change only this file. I have more partition. It is into /dev/sdb1