I'd get the barrel replaced with a higher quality one with a better twist rate and add some decent optics to the top for a designated marksman role. Lever action's much quicker than bolt and quieter than semi automatic
I love the tactical BAR. Some historical weapons are ruined when made tactical, but I think, with a little receiver milling to shed excess weight (shallow slots cut into the side like on a P226's slide) it could be made much better and lighter.
I'd love to see a tactical Bren with a G36 style double bollock mag on the top, it's be a laugh