This is a method I discovered to enter and freely explore Blackwater as Arthur anytime from Ch. 2 onward… no story mission glitches needed! I searched a bunch and haven’t seen this posted before, so I’m pretty sure it’s a new one. Apologies if someone has posted something similar before and I just didn’t see it.
It’s a long video, but the main stuff is explained in the first 5 minutes. Basically you just need a fast horse and need to have a lawman follow you from OUTSIDE of Great Plains across the border and into Blackwater. Then you just get all the cops to follow you around town until you lose your wanted level. Once you lose them, and as long as you don’t cross the town border at any time, you will be free to explore the town just like any other (with the exception that all the shops are perpetually closed, unfortunately).
Hope this helps and feel free to comment with any questions or add me on PSN… same name (Shermutt). Also PLEASE BE COOL, R* AND DONT PATCH THIS! Thanks! 🙂
Edit: As promised, here is the link to the video I used to help me get the Silver Dapple Pinto Missouri Fox Trotter Horse. https://youtu.be/bATG5JB9cNA
View original video here