https://github.com/RMerl/asuswrt-merlin/wiki/FAQ
Q: Does Asus know about this project?
A: Yes. We frequently exchange emails, and they have also integrated some of the features and bug fixes from this firmware project into the stock firmware. So far they have been quite supportive of this project, for which I am very grateful.
Q: Will flashing this void my warranty?
A: This is a kinda grey area for which I have no definitive answer unfortunately. I have seen Asus publicly commit to supporting DD-WRT for some of their models, without any mention about it voiding your warranty. Therefore my personal opinion would be that "No, it won't void your warranty", but as the saying goes, IANAL. Your retailer might certainly have a different view on this than Asus would, too.
NOTE: CSR Sanita, after confirming w/ her supervisor, said on 2/24/2016 "We will repair the product free of cost under warranty if it does not have any physical damage. No, it won't void your warranty."
Sent from Samsung SM-G965F using GAGT