Not true: DVD+RW discs are
not finalized, so you can still erase the whole disc later and start again. Even if they were, "finalising" closes a session on disc so it's readable by players that require it, but it doesn't make a RW disc become read-only.
I have Win7 64-bit, and a DVD+RW disc that I previously burned from an ISO image (i.e. it would normally be finalised if written to CD). I still have the option of adding more files to it and erasing it.