That doesn't seem like the type of thing you would want to keyword. The point of keywords is that they are a repeated mechanical pattern that players can mentally shortcut after seeing and playing with cards featuring it for a while.

This ability would be extremely oppressing in larger numbers and lower cost cards, making it unfit for prominent use, especially at lower rarities - which are what keywords are generally meant for as they lessen the overall mechanical nuance and complexity by generalizing/standardizing abilities and lowering the amount of raw rules text (where reminder texts don't count).

I think what you might be looking for here is a 'flavor word' as seen in cards such as Air-Cult Elemental and Blink Dog.

The idea was that writing "SandWing" in every SandWing's Creature type would make the creature type squashed. This allowed me to keep the flavour of the different tribes. If I make another SandWing (e.g. Qibli) they will have Poison Barb too.