It is almost impossible to reduce the sweetness of cookie dough once made, without further reducing the quality.
The closest you could come would be to create a second batch of cookie dough ingredients with reduced sugar, and combine it with your existing dough.
However, it will be difficult to achieve good integration of the two batches, and even if you do, the extra working of the first batch from the mixing will create additional gluten, making tougher cookies.
In this case, you might want to try some sort of tart lemon glaze or perhaps a very bittersweet chocolate icing to compliment your cookies and reduce the impression of sweetness.
On the other hand, except for butter, sugar cookies contain no expensive ingredients.
It may not be worth trying to salvage this batch.
In the end, this is probably a lesson learned that your particular recipe is not to your liking as is.
Next time, you will want to either reduce the sugar, or use another recipe.
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A (too) sweet cookie dough can easily be disguised or complemented by adding heat like cayenne pepper.
In my experience I added it to the dough and mixed it in.
(Second batch of cookies.)
Since you've already got your dough mixed working your dough is just going to end up with a tough dough.
I've found the combinations of chocolate, heat, and sweet or lemon, heat and sweet work very well.
Make a glaze or frosting.
Add the heat to disguise or complement the sweet.
I don't think it's a good idea to bite directly into the heat, particularly, when one is expecting something sweet.
I'd experiment with a few of the cookies.
First test - Use a very very light sprinkle of the cayenne on the raw cookie dough, press it in so it doesn't just burn on the surface, bake the cookie, frost, taste.
Second test - separate some of the glaze or frosting from the main source, add a very very light sprinkle of cayenne to the glaze or frosting, mix thoroughly, frost a baked and cooled cookie, taste.
Adjust to your preference.
You should end up with heat but that is an after effect.
Sweet with chocolate or sweet with lemon are the first impressions, a few chews and one becomes aware of the heat.
cooking.stackexchange.com/users/52926/Rose
A little suggestion, if I may.
Mix your remaining dough with no flour, some soft butter and corn flakes.
Work the dough gently and form your biscuits as usual (try using a spoon to put them on the baking tray, since the high content of butter makes the dough very soft) and finally cook them - though a bit less than usual.
You'll get biscuits with a pleasant, sweet taste, but slightly salty and in proportion to the other ingredients there will be less sugar.
I often use this trick to save dishes with an excess of a certain ingredient.
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My attempt to bake chocolate chip cookies from a store bought log came out too sweet.
I added a small amount of lemon zest and a few drops of peppermint flavouring to the next dough log.
The cookies are much better.
cooking.stackexchange.com/users/50581/Chirpy
When my chocolate cookie dough was too sweet, I put crushed walnuts and hazelnuts on top of the dough before I baked them, and when they came out of the oven I sprinkled a tiny bit of salt on top of the cookies.
This helped tone down the sweetness a lot.
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I made my sugar cookie dough too sweet, and I just added lime juice and salt to a cup and mixed it well, then mixed it into the cookie dough, and the cookies came out really good.
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Adding oats and nuts help to lessen the sweetness of the batter :)
cooking.stackexchange.com/users/84972/nahkh
I just baked the first batch of cookies and I found them to be too sweet to my liking.  The remaining dough is sitting in the fridge right now and I was wondering if there is anything I could do to it to reduce its sweetness.  These are the simple sugar cookies,  btw.
How to salvage a cookie dough that is too sweet?
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cooking.stackexchange.com/users/6640/Uday Kanth
It is difficult to correct this, but you could mix in a second batch with reduced sugar, use a lemon glaze or bittersweet chocolate icing or add lemon, cayenne pepper, oats or nuts. While you can't reduce the sweetness of existing dough, you can try combining it with lemon zest or peppermint flavouring.
You can't reduce the sweetness of existing dough. You can try combining with lemon zest, peppermint flavouring or cayenne pepper.