Is there any way to assign keystrokes to Stage Lock other than Alt-L?

[NeoMorph]

I want to use stage lock controlled by a joystick adaptor but it's looking like it's hard coded.

Is there any way to override it?

[Alshain]

No, re-bindable keys are incredibly limited in KSP

[Crown]

This might be a strange and overkill solution for what you want:

There is a program called AutoHotkey which can be used to reroute keys (For something like pressing a single button to write "Dear customer, " and other stuff). I don't know if it will work with your joystick and you might need to read a bunch of stuff first - you basically write a little program. But that's the only solution to trigger a Alt+L without changing KSP's code that comes to my mind.

http://www.autohotkey.com/ is the website. This program might be detected by some virus scanners as a key logger, which it is essential. But it only does the things you tell it to do. So it's safe.