As always the answer is It depends. The MAC itself doesn't do anything specific that makes it more difficult to replace the hard drive. All you need to do is open the computer pop out the old hard drive and put a new one in. Of course it depends on which version of the Mac.
You have all modern computers aiming towards thin and light have become less repairable than older computers. If you have a Surface Pro Windows computer or a new MacBook Air, neither one of them is going to make it easy for you to repair anything inside of it. There's just too much glue.
With most laptops older than a year or two, you should be able to unscrew it take it apart and replace parts. A couple of words of wisdom. If you want to fix any Mac, check out the website by Ifixit. That is IFXIT.COM.
They have instructions on doing all sorts of repairs for every single mac that can be repaired. The second word of wisdom is if you have an iMac, don't even try the iMac. It requires you to use suction cups to pull the screen off there's a million pounds of glue inside, and wires that connect things up that are apparently the same size as the hair of an angel. So if you have an iMAC and it's not one of the old ones, that's pretty thick, I would recommend letting a professional replace the hard drive for you. I have a bunch of old Macbook computers, the old plastic white ones, and I've taken those things apart from front to back replaced every component and it's easy with the help of Ifixit.com So can you.