Use the LCD to display a menu system and use the IR Remote to
interact with your menu system then the IR remote needs to be used to type in a passcode which will unlock the menu system. then the IR remote needs to be used to navigate around your LCD menu and select which value you want to change and then change the value. You can use a single IR remote input button to exit the menu system.
i have so far got the vlaue of my ir remote button
you need some sort of a state machine where you never have blocking code or delays
you start in the locked mode
loop()
if you get a key press KEY from the remote
if in locked mode
add KEY to a buffer (or clear buffer if you have a clear key or max length)
compare with the unlock code
if this is the same
record that you are in the unlocked mode
else (you are not in locked mode)
apply KEY to your menu system and trigger the right function
I assume one of the function in the menu will lock again, it's just a matter of recording that you are in locked mode.