Very much so. MP3 yi-universal lossy codec - akukho nto ithintela ukuyidlala, ngexabiso lomgangatho ophantsi nge-bit nganye kune-AAC okanye i-Opus. That determines both the headroom available and whether the saving costs you anything in fidelity.
Yes — Ii-frames ze-MP3 zii-blocks ezinobungakanani obumiselweyo, ngoko ukutywina kuwela kumda we-frame kwaye abaphawuli bokudlala abangena-thuba ababuyi kuqhubeka nokuphinda bakhowudi. It is worth knowing before you overwrite an original you might need again.