Depends on how you access them
F.ex. if you are using “OnBeginOverlap” - it returns much information and you can use a Cast to affect only selected BP’s
If only one Char overlaps you and you cast to it - you are referring to the one who touched you
If you use LineTrace - similar thing - you get info about what the line encountered on the way and if it hits some Actor - if you Cast to them you will be able to change them as you wish
There are nodes like f.ex. @Everynone suggested - Get All Actors of Class but you can imagine what that one will do if you loop through All existing Actors of choice ;]
But basically once you get a Reference to an Actor - you edit it directly
How you access it - it’s another story