Yes - the MM and DMG give tips on adapting the stat blocks.
On page 342 of the MM, in the "Appendix B: Nonplayer Characters" chapter, there is a section about "Customizing NPCs". It states:
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.
Furthermore, the DMG has a section on custom NPCs on pages 279-283. On page 282 specifically, there is a list of various races (including some monstrous ones) and their corresponding stat changes, so you get a quick overview instead of having to comb through the PHB.
Note that when using this table, if you change the ability scores of an NPC, you might have do adapt his CR, as stated on page 283.
In your example, the scout stat block specifically lists as its race "Medium humanoid (any race)", emphasis mine. Consequentially, I would give the scout the corresponding racial traits (such as darkvision), but not change the given ability scores.