JDBerg said:
... Does not teach gunsmithing but has forgotten more about tactical shooting under combat conditions and competition shooting than the rest of us will understand!
You're right, we'll never understand how much he has forgotten... 
but nothing that he may know or has forgotten really addresses the consequences of modifying one's guns, or analogously, one's car, computer, car computer, or any other machine. Being a cop, a Marine, or a successful competitor doesn't really make him all that different than many participating here. As best I can tell, the credentials you cite, while impressive in some respects, still don't make your friend more EXPERT than others here when dealing with the topic of this discussion -- safely and effectively modifying and (hopefully) improving personal weapons, or the legal consequences of having done so.
As to related legal issues: we HAVE had a lot of discussions on the legal problems associated with gun modification when they are used in self-defense shootings, either on this forum or The High Road;
Mas Ayoob* has participated in a number of the discussions. As I understand the gist of these discussion, two points seem to stand out:
1) if it's a "good shoot" (i.e., the person using lethal force was justified in doing so) he or she is unlikely to face
criminal charges even if the gun was modified, but...
2) The "victim" of such a shooting, even if he or she serves jail time for the act(s) that prompted the "justified" shooting, can sometimes still file a civil suit against the shooter in some states. In some cases he or she might even win. Here in my state (NC) firearms laws protect the shooter from CIVIL suits if it was a "legal" shooting, regardless of gun modification or other incidental damage.
In other states, the story might be different, and it's up to the individual to know what s/he faces in that respect. THAT is an argument YOU should be making -- as it's a valid point, but only if the gun in question is used in a "lethal force" shooting. If the gun is used only in competition or at the range, it's a non-issue.
Switching from one form of factory part to another from the same maker -- which is common among Glock users, seems to NOT be a legal or functional issue. Using a gunmaker-approved or importer-approved (or recommended) after-market part in a Sphinx seems to be little different. And as WVsig noted, the Sphinx pistols that prompted this discussion, after modification, are less "modified" in terms of ease of use and safety than some well-accepted factory-direct pistols in stock form.
A key point remains:
you don't know how much others participating here know. The knowledge and skills you attribute to your expert friend can also be found in a good number of people participating on this forum, many of whom also disagree with your position and the position you attribute to your friend. Your friend is certainly welcome to speak for himself, here.
If he (or you) can do so, you (or he) should feel free to cite some legal cases or real-world events (and their consequences) that inform the positions you (and he may) have taken. Then your position might seem more valid. I suspect that if your friend does participate here, the gist of what he shares with us will come across with subtle but important differences. As you now present your case, it seems mostly based on emotion or fear than anything else.
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*Mas Ayoob is a recognized expert on the use of weapons in police and civilian shootings. He has single-handedly made himself a recognized expert; he has also spent years doing it, writing articles for major gun magazines, and teaching classes for effective self-defense and his views on the related legal issues. He also works as an auxiliary police officer.
Unhappily, there is no certification process for HIS sort of expertise, and there doesn't seem to be any others who even try to do what he does. So in his presentations and opinions, which often make very good sense, but it, sadly, only ONE point of view for THIS SIDE of the debate. Folks accept (or give serious attention to) his opinions because it's about all they can find. I wish there were more experts and some additional or different perspectives on THIS side of the topic.
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