Are they accepting walk-ins or only by appointment?

You can definitely do walk ins, you just have to do the prescreening first and wait in your car until they come out and get you.

Walk in and appointments

Either. Everytime I have gone, it's been without an appt. Just scan the QR code at the door (pre screening) and they will call you in first come first serve based on service you're getting done. I think you can call or email them if you have any questions or help on custom work.