If one has perfect vision, is it bad to use reading glasses; will it mess up the perfect vision?

Shouldn't: All depends on what you define as perfect vision. If that has been assessed by an eye care provider, then reading glasses are merely extra magnification and shouldn't interfere with your vision. However, if you have any residual farsightedness or other type of prescription at distance, sometimes this can become more manifest, or noticeable, after wearing reading glasses.