You also completely missed the point of my response. I specifically brought out the context of the MD ruling because of what it responded to: a simplification of the attacking process beyond even what you describe the pen dagger to be. It is quite literally click and drag onto the target (assuming safety is off). No response, no indication. Truly invisible (especially if the silenced pistol could do this).
The boot knife, as far as I'm aware, can be drawn using an action in the top right window. The object tab iirc. I'm not entirely sure on this, but my point isn't hurt by this either.
A gun can do this just as well. You press H, ensure you're on harm intent, and click. RNG is the only savior for the target. The downside being it's visible.
Take another example, a butterfly knife. Butterfly knives can sit in your pocket, which isn't revealed by examining. Click, activate, viola a knife. Most people can do this very quickly. Small guns can do the same, even removing the step to activate it. Just click from the pocket and harm intent click. This is so common, many antags and secoffs do this with great effect.
It is not particularly different to any other weapon especially the concealed cane which is already in the game.
TG is the inspiration of the idea, but thankfully we have the ability to modify how things are implemented as we desire. There are ways to address, you had one idea. Add an extra set to convert the pen, then activate it to turn on the laser blade. The benefit is that if you're searched, it's concealed. No one will know and you get to keep it, which is better than a boot knife which can be found (and requires a boot), or any other manner of weapons that are overtly weapons and would get you arrested/searched. That is the trade-off. Concealment for quick easy use.
Either way, I think it's a neat idea. I'll leave it to the maintainers to decide either here or in a PR if one is made.