What parts would these be? Something coated with the actual metallic paint used inside the early 128/512K compacts and HD20? There have been multiple reports both here and elsewhere of the dunking method not harming that particular coating in any way whatsoever. My own experience has been that the coating is not affected at all. However, this is all moot as daver_cl has the reactive metallic coating as do most SEs.
Also, H2O2 DOES NOT react with ALL metals. If you recall the discussion, the original square Apple logos on the 128K & 512K were immune to being submerged in an H2O2 bath, whereas the newer inlaid Apple logos were made of something highly reactive to the corrosive effects of H2O2. Since H2O2 does not react with stainless steel or aluminum, it was decided that the early square Apple logos were made from more expensive pressed aluminum, and the newer apple-shaped logos from some kind of steel. So it all depends of what the "metal specs" are comprised. I would not be one bit surprised given Apple's use of aluminum chassises for FCC mandated shielding prior to the Macintosh, that the paint they coated the inside cases with wasn't also an expensive aluminum based paint. The later shiny, smooth coating was probably a cost cutting measure (during the greedy Gassee years), as the FCC guidelines were less stringent by then, and it not only looks cheaper, but it probably isn't aluminum either, at least not 100%.
As always, your words of warning or caution are always welcome. Someone making decisions about their equipment should be aware of all potential problems they face when working with such volatile products. Your points about the paper labels are well taken. Then again, those labels will continue to change over time anyway thanks to the adhesive used to apply them and can't really be restored (the best would be to scan them and create replicas). This has also been discussed at length here and elsewhere. They agency labels have also been discussed and are not affected, and as I pointed out, if they are yellowed too, will look pretty bad against a newly de-yellowed case. However, this is for the original 128K through Mac Plus, so one cannot guarantee it on an SE. If the label is not yellowed, then why risk it? If it is yellowed, then test a narrow area along the edge to see how it reacts.