Though I have not nearly as much experience as the fellow users who contributed to the discussion, I would like to put my two cents in.
When I first resolved to erase the print off some parts, I went with the pen eraser method, following a suggestion I’d read on some blog. To my dismay, the results left me deeply unsatisfied. Not only did the pieces end up looking significantly duller, scratch marks were also very much visible. Coating the pieces in hair spray restored their shine, but the scratches stayed, and to my eyes they looked very much unpleasant.
I could not ascertain what went wrong: the eraser was precisely like those I would later find shown in this thread, a blue/red one. I hardly think I applied too much pressure – I endeavoured to rub as gently as I could – though I cannot entirely rule out this possibility. At any rate, disheartened by such an outcome, I abandoned the idea of removing prints altogether, lest I ruin other perfectly fine pieces.
At the end of January, I purchased some klickies which were – let’s say, not so clean. In particular, on an old janitor torso there was a blue mark which would not go away with soap; so I decided to resort to alcohol. I grabbed the alcohol bottle, poured some on a cotton pad and rubbed the torso with it. To my utmost surprise, the mark was not the only thing to disappear – the print was beginning to fade too. I kept it up and succeeded in completely removing the torso print without the slightest semblance of damage to the part.
In the following weeks, I continued to employ this method on a variety of parts: as of now, I have successfully cleaned torsos, arms, legs, headwear, and vests. I have not yet had the need to remove facial hair, but I presume it wouldn’t be any different.
The only somewhat significant issue I’ve found might arise from the fact that parts which undergo this treatment end up being somewhat shinier. I’m not positive I could manage to capture it in a photo, so I’ll try to describe it in words. One of the parts I used as a testbed was a misprinted bulletproof vest. I only erased the bottom silver part, leaving the “POLICE” writing intact. Upon close inspection, the middle and top portion (which I did not erase) has somewhat of a grainier texture and is slightly more opaque than the part I erased; the latter looks smooth and even somewhat more intense in colour. This effect is only noticeable on parts which have the grainier texture I’m striving to describe; some torsos (old and new alike) do, but this is mostly the case (from my limited experience with the parts I tend to handle most) with the blue and grey bulletproof vests.
For the sake of full disclosure, I feel the need to say that, depending on the print, it might take a while to erase it – especially if there are multiple overlapping colours. Some appear to be harder to remove than others (silver, for instance). In spite of that, at the time of writing, the method I described is the only one I feel comfortable with, and wanted to share in case anyone fancied to try something different.