My main two points are thus:

1) I'm doing my utmost to avoid killing off your character. I hate it when people kill mine, other people hate it when people kill theirs, and thus the Golden Rule applies.

2) Shell Shock doesn't have to 'morality' anything. Even a 'if you don't see me do it' loophole would get him out of dangers that aren't even dangerous in the first place. The bluff doesn't require a change in lifestyle. If he's really that afraid of the possibility that he‘ll explode, the only thing he actually has to do is avoid blowing up a bunch of people in public. And considering Bridle Shores is still standing, that frankly doesn't seem like much of a stretch.

From what I’ve seen of Shell, his attitude as the ‘meh’ mercenary makes the concept that he would be browbeat by shunning from Fox Trot and Grills (ponies who, as far as I know, are acquaintances at best) is a bit absurd. And his status as a competent combatant with a bunch of explosives just burning a hole in his bags would take the phrase ‘fudge the police’ and give it a brand new meaning.

Meaning that so far, his consequences are:

1) A bluff that, while he may fear for a time, he barely has to cop to and won't do anything when called.
2) The anger of two ponies which, while possibly hurtful if they're more than acquaintances, doesn't actually mean anything if he doesn't actually care.
3) Metaphorical flies on a windshield, if the police even suspect him at all (And no survivors means low chances).

Which means that, in turn, the negative impact of the loss of potentially hundreds of lives is just Roleplay fodder. And that’s really what it all comes down to. This isn’t railroading. This isn’t a straight-shot plotline. This isn’t a ‘do or die’. The entirety of what comes next in Shell’s life is up to Shell. Whether he plays it sneaky, plays it safe, repents, continues on, calls the bluff…that’s all on him. This detonation thing is just a byword, Grif. I’m handing you a map.

Which direction are you going with it?