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. 