Ok, as far as weight, yes it will be lighter by simply changing the stock, but the overall weight will ultimately depend on which accessories you add.
Accuracy will be unaffected, or in some cases may improve as long as the stock has a tight fit. Most synthetic stocks are designed for this.
Now keep in mind, once you change the stock the gun is no longer in original configuation and must be 922r compliant which means you are going to have to change out some more parts and probably remove the grenade launcher and sights. If you like the T-6 stock the first link below has a kit that comes with all the compliance parts you will need, otherwise, you will probably have to purchase everything separately. I also recommend getting a new gas tube with the synthetic handguard already attached. The second link has them in stock. Just make sure you order the one for the Yugo. The third link is a SKS specific forum where you can find out about all you want to know about modifications and compliancy.
http://www.nationlink.net/sksman/
http://www.tickbitesupply.com/sks.html
http://www.websitetoolbox.com/tool/mb/surplusrifle?forum=4870
I am attaching a pic of a Yugo that I picked up at a pawn shop. It was in such bad shape it wasn't even on display. The only reason I got to see it was because I was looking for a fixer-upper for cheap. The only way you could tell it was a Yugo was because of the gas tube selector. Everything was removed from the barrel including the front sight assembly
It had what was left of a folding stock and pistol grip ( the folding butt stock had been cut off as well). I put it in a ATI Monte Carlo stock, added the necessary compliance parts, a ScoutScope mount, Simmons 4x32 pistol scope, a compliant muzzle brake, and some touch-up bluing. I also have a bi-pod that sometimes I use and sometimes I don't. I finally found a front sight assembly which should be arriving next week. I hope this helps with your questions.