I assume you mean putting new cable including housing in, correct? (if just the inner you should be able to easily push a new inner through the housing).
On my only bike with this set up I tied a string to the cut end of the old housing and pulled it through, tied a washer to each end to prevent loss. Tied the string to the new housing when ready and pulled it through. Its not a huge drag, and this worked fine but I did eventually figure out you can pretty easily fish a stiff wire through (if you are patient)