BUUUUUUUUUUUUMP
This use to be a mad pain in the ass for me aye, had hundreds of gb worth rip
FIX:
If your mods are updating through steam you can trick the shit. step one:
make sure you have the download running. Then click on arma 3 and press play. A pop up will appear and then you want to tick this box.
Launch games as soon as its ready
step two:
Go into your download tab and pause the download
And as soon as you've done that the game will launch :) A mate showed me this so I don't take any credit it for this cheekiness!
Shizzly / MaccaWrappa