i'm trying to make a sword with custom damage

so i've got a function that gives this the proper damage value of 5.5 with attribute modifiers
problem is i've gotta run that function myself with /function
does any1 know how i can make it properly run every tick, i tried via adding the function to the tick tags but that requires me to change the function to use @a instead of @s which is a problem cuz since i'm setting the proper damage values with item replace, i'd guess that in multiplayer everyone's mainhand items would get replaced with this sword, which is BADDD,,,