Though it's not illustrated in this thread, Nevermore's done a lot of research on the subject of Spychangers, revealing that the proper spelling of the name is indeed the single-worded "Spychanger", rather than the two-worded "Spy Changer" that popped up a few times in the 2000s and, thanks to TFWiki using it for the longest time, went on to influence some minor fictions by Fun Pub.
As seen in the collage below, the single-worded spelling originated from the cartoon's production bible, the title screen for the episode "Spychangers to the Rescue", and was finally used by Hasbro proper for the Walmart-exclusive Universe 2-packs of Optimus Prime w/ Prowl and Ultra Magnus w/ Ironhide.
However, in the time between all that, the two-worded "Spy Changer" spelling was used for the KB Toys/Target-exclusive clear redecos of the Spychangers, the KB Toys-exclusive G1-colored redecos that had a generic subtitle-less "Transformers" logo, and the dollar stores-exclusive Universe-branded rereleases of those G1-colored redecos.
To make matters more confusing, at the same time as when KB was selling those G1-colored "Spy Changers", there was a KB Toys catalog that instead called them "Spychangers".
Something else to note is that, when the RID2001 line proper was being sold at mass retail in 2001-2002, the Spychanger 2-packs did not actually use the name "Spychanger" or "Spy Changer" at all. Instead, those 2-packs were simply labeled as "Basic class". The "Spy Changer" name wasn't first used by Hasbro for any toys until the 2002 KB Toys/Target-exclusive figures, which were single-packs instead of 2-packs.
What's more is that the main RID2001 line had each Spychanger sold in a 2-pack at the Basic class, while the rest of the line's Basic class consisted of single-pack Decepticon Commandos (a cartoon-only name), the single-pack small-sized Optimus Prime and Ultra Magnus toys, and the redecoed Beast Machines Obsidian mold.
Now, out of all of these toys, fans have referred to only the toys that were sold as 2-packs, plus the Optimus and Magnus toys, as Spychangers. However, I feel it has become a misconception to refer to the Optimus and Magnus toys as Spychangers, since while they were built similar to the Spychangers in how limited their articulation was (and because they were both new-mold Basic class toys just like how the Spychanger versions of X-Brawn and Scourge were), there actually has never been any official labeling of those two as Spychangers from Hasbro.
As stated before, the original toys themselves were simply labeled as "Basic class", and when they were later redecoed and released in the Universe line with the Prowl and Ironhide toys, only Prowl and Ironhide were called out as Spychangers, while Optimus and Ultra Magnus were not. Specifically, the two 2-packs were named "Optimus Prime with Prowl Spychanger" and "Ultra Magnus with Ironhide Spychanger".
Furthermore, the RID2001 release of Basic class Obsidian featured a cross-sell on the back of its packaging that showed Optimus and Magnus to be part of the same assortment as Obsidian, and he certainly wasn't a Spychanger.
