What headphones are you modding?
As for sleeving it's pretty easy, it can just be time consuming to "inch worm" the wire through the sleeve.
With paracord you're going to have to cut the ends, pull up the kernmantle rope just enough to grab (without fraying the nylon too badly) melt the nylon slightly and then pull out all of the kernmantle. It's a also good idea to cover the tips of your cut wire with masking tape before threading it through the paracord to prevent it from snagging or getting stuck.