The usual trick when renewing wires is to use the old one to pull the new one in. Need to ensure the two are joined effectively. At least twist together the central cores with pliers and get some PVC tape over the joint, trying not to create a bulge. I'm presuming there is an old coax in there. Get someone to help, one pulling gently, one feeding in. You do the pulling then it's your own fault if the joint comes apart!
red.