In the Star Wars universe, numerous actors have become forever connected to the characters that they play. However, Donnie Yen was even more involved in making his character his own. Apparently, Gareth Edwards gave Yen a free hand in fleshing out his character, and it was Yen's idea to make the Force-sensitive monk blind.
Donnie Yen was profiled by Jetset Magazine when he revealed that making Chirrut Îmwe a blind character was entirely his idea. While actors are usually given some leeway in building their characters, changing somebody who was apparently written as a character with sight to make him blind is less usual. That sort of thing could potentially have repercussions that require script changes in order to make it all work. It's not clear how much of the rest of Rogue One: A Star Wars Story had to be changed to accommodate a blind character, if any.
For whatever it's worth, it would appear that this is an example of Lucasfilm being more open with their expansion of Star Wars than many would have believed. While many would suspect that Lucasfilm is keeping tight control over the universe as it expands, in order to be sure it does so to their preconceived design, everything we've heard is that such is not the case. Writers and directors are being given freedom to create their visions however they wish. This apparently includes deciding which characters have use of the ocular nerve and which do not.
As with much of Rogue One: A Star Wars Story, a lot about the characters is still shrouded in mystery. All of the trailers have focused on Jyn Erso, and we've only been given a passing introduction to the rest of the team., We know that Donnie Yen's character is the closest thing to a traditional Jedi that the film will have (outside of Darth Vader, of course). He's a monk who does not use The Force but is sensitive to it. It would appear that he uses that sensitivity to aide him due to his missing eyes.
With just over a month to go before Rogue One: A Star Wars Story hits theaters we're waiting to see just how popular this unique Star Wars film actually will be. While the story of stealing the Death Star plans is connected to the traditional saga, it's focus is entirely new. Even the other Star Wars Anthology project that has been announced, a movie about a young Han Solo, will deal with characters that fans are familiar with. Nearly everything about Rogue One is new. While the movie will certainly see some level of success simply for having the Star Wars name, with it following the smashing success of Star Wars: The Force Awakens it's already following in some big footsteps.