I think if I were to start a new town, I'd change them depending on what theme I settled on. But for my current town, my paths remain the same all year round.
I will keep the paths unless I get tired of them. Around the holidays I like to add some special path, such as fireworks for fourth of July or Santa path at Christmas. I've put a lot of time into looking for the path that is right for my town.
I don't use the same paths when restarting or making a new town but I use the same or try to stick to a specific path a lot longer if it's the same town (like I don't change them 'cause of seasons) but I like mixing those paths and having variations.
I always change mine. Even if I'm not resetting, I just change mine every season to have a new look for the town. Keeping them gets boring after a while.
New paths. Also, I've decided I don't like the effort of paths that take more than 1 QR code. If it only uses 1 QR code spot and I get bored of it, it's also easy to get a new one - just replace the old code with a new one. Bam! New path design, no laying down a new path.