If you use multisession, then you can do this with both CDRs and CDRWs.
However, every time you make a change, you lose 35 MB, and you do not recover the space which the old file used.
If you have used a CDRW disc with multisession, then you MUST use the full erase option, before using it as a fresh disc - if you only use quick erase, then very strange things can happen.
If you want to use a CDRW disc as a large random access removable disc, then you need InCD.