I had an idea for non lethal skin mutations, examples: dandruff, seborrheic dermatitis (eczema) & psoriasis.

The mutation would not be visible in cubs, the lion may or may not experience pattern baldness due to itching during adulthood.

If you didn't use the falcon's eye for the mutation the only way you would know about the mutation is if you have an interaction popup for example, "You've have noticed your cub/lion has been scratching itself a lot lately but it doesn't have fleas.", "Your cub/lion has been complaining to you about constant itching." Or "Your cub/lion asked you to scratch an itch they can't reach, you give them a good scratch but they said there was no relief".

Also with this males can still patrol and be kings, females can still hunt and breed, and they both live the lifespan as a normal lion.

(Update: I removed the aloe vera idea since people don't like it and find it similar to wolvden. )