I just brewed my 3rd batch ever, so I'm not very knowledgeable, but I personally wouldn't go to that trouble, replacement.
It wouldn't really save you any time and I don't think it would cut down on the risk of contamination either. If you don't get a great seal on the hole/plug, you'd open yourself up to more problems too.
If you just sanitize what's going into the brew, you'll be fine. Personally, I use a wine thief and find that to be much easier than anything I'd tried.
Then again, I'm pretty sure I'll never take a SG reading while fermenting ever again. I did alot with my first 2 batches though.