If you use vinegar to preserve a piece of bread by pouring it over, will the vinegar affect the bread's taste?
Yes, most varieties of vinegar (all the ones you would use for preservation, at any rate) have an acidic taste, which is imparted to the foods preserved with them. Additionally, if the vinegar has a flavor (e.g. red wine, sherry, ...), it will also affect the taste.
It's sort of inevitable, given that vinegar is a diluted acid. You can mitigate this by adding salt, or further diluting the vinegar with water (though the latter affects the preservative properties of the vinegar).
In any case, I would not recommend using a liquid-based method to preserve bread, as it'll probably promote mold growth more than inhibit it, or ruin the texture of the bread. You usually want to use dry preservation methods (e.g. wrapped freezing), or incorporate the preservatives (such as a sourdough starter or vinegar) into the recipe prior to baking.
Are you trying to extend the shelf life of your bread? or are you doing a scientific experiment?
Salt is the traditional ingredient added to bread to extend shelf life. Today there are modern preservatives, but bread artisans shun it.
Vinegar is acetic acid, and you could use it as an ingredient when baking. It will slow down the yeast, but if you don't add too much you should be fine. If you want to try a different acid you might go with milk. It has lactose sugar, and if you use a sourdough starter the lactobacillus bacteria will convert lactose into lactic acid giving it a tangy sour taste as well as extending shelf life a few days from mold growing on the bread.
If by chance you are using a chemical leavener instead of using yeast you'll need to adjust your recipe to account for the acid and alkaline balance. Baking powder is ph neutral when activated. If you are adding acid you may need to switch to baking soda instead of baking powder during the leavening process as you figure out your CO2 gas vs desired acidic taste balance.