I take articles published by companies selling insurance with a grain of salt. These authors often use situations where modifications were admitted as evidence in a civil trial to imply that there could be criminal implications for other gun owners. While certain modifications would expose gun owners to civil liability in cases of accidental or unintended discharges, the same is not necessarily true for cases involving legitimate self-defense.
I have been asking attorneys for years to forward me any information concerning the issue of legally modified guns being successfully used against defendants in criminal trials. Evidence of illegal modifications (short barrels, auto-firing mods, removal of features required by certain state, etc.) is used against criminal defendants on a regular basis. However, I have yet to find a case where a legal modification to a legally-owned firearm has resulted in charges being filed that would not have been filed if the gun had not been modified.
I would not personally plaster offensive slogans and Punisher skulls all over my guns, and would advise people doing so that it could possibly have negative consequences in civil trials or criminal investigations of questionable shootings. However, I have yet to find a situation where an internal mechanical modification, or exterior ergonomic modification, to a firearm has had any affect on a criminal case involving self-defense. This article tries to use the prosecutor's statements in the George Zimmerman trial to support their position, but fails to mention the obvious fact that these statements did not sway the jury and Zimmerman was not convicted.
As the article mentions, modifications can affect civil trials based on negligence. These trials almost always involve situations where an unintended discharge caused injury to persons or property. In cases where someone has removed a safety feature (especially an external or "drop-safety", or a magazine disconnect) the modification is very likely to be admitted as evidence in court.
I apologize for the lengthy post, but I have been following this issue for some time. If any forum members have personal knowledge of this type of evidence ever being successfully used by prosecutors in criminal court, please let me know.