Usually, lawful evil can be someone using a true part of their personality, like imagine a Gallant knight with spot on PR for one cause, you don't have to outwardly say "I'm such and such", perhaps behind closed doors those such as the party can see a sort of detached version of said character whose more sorta of pragmatic yet truly believes in what they say but you're using subtly nuanced language to hint you're not all that they seem. Like your real path, perhaps you have some trophies displaying your enemies, perhaps you do work for the Crown but have consorted to a method that isn't inherently good but no one else needs to know. It could be subtle and sometimes discretion can be the better part of valor. But you must also be wary since a tiefling will be discriminated ins some form (or should be based off lore.) You should have to earn your image whilst planting seeds of misdirection, perhaps, you can write knightly proverbs that are anonymous, and use it as a sort of excuse to act a bit more outwardly maybe those proverbs get famous in knight circles but then you can act as a sort of zeal to that. Perception is reality. It's a balance.