Damiansmith is correct,
The roof rack is far from permanent, but is most definitely more of a hassle to take off and put on than a basic trunk bike carrier.
On the other hand though it is not difficult either. My brother puts his roof rack on his BMW only when he is taking his bikes somewhere and removes it immediately after he's done with it (every now and again he'll have it on for a few days or maybe a week before removing it) He must install and remove the rack during the riding season maybe 30 or 40 times...
You need to be a bit more careful when mounting it too as a slip and having a part of it bang on your roof could cause more paint damage than a months worth of the worst trunk lid rack on your trunk 🙂 But even if your're only moderately careful, you should be fine.
In addition, as my brother is FANATICAL about the condition of his cars, he has these thin black semi-adhesive squares of what seem like metallic material that are stuck on the roof of his car that the rack towers sit on THey remind me of the consistency of license plate registration stickers but not nearly with the same adhesive properties 🙂 They peel off as easy as yellow stickies, leave no residue and completely protect the clear coat from scuffing due to vibration even though the pads on the bottom of the towers do this pretty well... His BMW is dark green and the stickers are black but he says they also come in different colors so that if you match your car paint even halfway and leave them on they're difficult to spot unless you're looking for them...
He's been using his roof rack for years with these methods and I'll be damned if I can spot a single anomaly in his roof pain where the rack sits...
Good luck!