It's hard to be sure from the code fragment above, but it looks like you're only doing the blinking when you detect a key from the remote. My assumption from the OP was that you want to flash the LEDs continuously, but have two buttons on the remote that change the interval. If that's correct, just put the interval adjustment code inside the if that detects button6 and run the blinking unconditionally.
I'd suggest that you just increase interval when you detect button6 to start with. That way hopefully, you'll see something working, even if it isn't your full requirement. Incremental development FTW!