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From MM342, top left corner:

Customizing NPCs
There are many easy ways to customize the NPCs in this appendix for your home campaign.
Racial Traits. You can add racial traits to an NPC. For example, a halfling druid might have a speed of 25 feet and the Lucky trait. Adding racial traits to an NPC doesn't alter its challenge rating. For more on racial traits, see the Player's Handbook.

To answer Mr. Adventurer, there is no need to adjust an NPC's ability scores. You should only do so if you feel the change would make a meaningful difference in the NPC's impression upon the characters.