If I want to reduce the amount of sugar (to reduce sweetness) in a cookie recipe, how would that affect the end result (mainly with respect to texture) and what can be done to negate it?
Sugar isn't added to baked goods just to sweeten them: it also does things to the fats and starches to help create the texture. This is related to why some recipes require castor sugar (i.e. very fine crystals) and others do not.
One solution you could experiment with is changing the sugar. Dextrose is noticeably less sweet than cane sugar, for instance, for the same quantity.
Sugar works as a tenderizing agent in baked goods. Since water loves sugar, they bind together, adding a bit of moisture. It's probably ok to reduce the sugar by 1/3 without seriously affecting the end product. You may need to add a little more fat (as a tenderizer). I suggest experimenting with your recipe, reducing the sugar a little at a time until you come up with an acceptable end product.