You either added the baseitems2da as a hak (and in that case this mod simply does nothing) or you didn’t and this mod will work as intended, it’s only one file, in either case it won’t “break” anything.
The statement about stack affecting cost values in a store is not correct, it’s the ILR stack size that affects the worth of items, but this mod leaves those values unaffacted. Obviouslly, 9999 arrows will sell for more than 99 arrows, that much should be obvious.
I corrected my post, as you are correct about it being added as a hak (prioritizing over override). Thanks for pointing that out.
With reference to stacking and costs, I thought I did notice something was affected in my own testing (not of yours, but my own). I will double check that then … thanks for the feedback.