Yes, there are three differences between a furling and hank on sail. Furling sails have a bolt-rope, a sewn-on cover, perhaps a foam luff to shape it when reefed, and they are cut somewhat different than hank-on sails.
If a hank on sail is near the end of its life, it may be a candidate for converting just the luff. Know that, uncovered, the sail will rot in the sun… but it’s near the end anyway, right? Get a couple more seasons out of it and then buy a new sail.
If the sail is fairly new, the inclination is to convert it. But add the cost of conversion, the cost of the cover, plus the used value of a good sail… Is it better to sell it and put that money toward a new sail that is purpose built to be a furling sail? You decide.