It seems i can't manage to increase stack size of javelins either manually nor by adding an affix 'increased stack size'. Affix just doesnt save into the game itself - stack size remains the same and the affix doesn't show up on item, and manual change of quantity only increase current quantity only, not the stack size.
I only wanted to save so much of coming back to town trips for repairing my javs which i found during a playthrough I am currently at without like breaking the game rules.
So the solution i came up is duplicating javelins itself, but if you want to look at this it would be great :) if not i can live with duplicated 2 packs of Javs :D
great work!