I will say that stoning internal lockwork is seldom a good idea, and has ruined far more revolvers then it’s helped. I would strongly advise that you don’t touch the ratchet teeth because again it is likely that you’ll get into more trouble then you’ll get out of.
As for the warrantee. If you send in the gun they will quickly notice what’s been done. If the trigger pull roughness is being caused by something you and/or your friend did then obviously they are not obligated to fix it for free. But if it is a problem that pre-existed before the revolver was worked on, and is being caused by something that goes back to when the revolver was assembled in the first place, they are far more likely to fix it.
Apparently your friend did do something to the hand, and maybe the slot in the frame it moves through. If he didn’t get carried away when it came to working on the slot in the frame (which is generally something you don’t do) they might decide to replace the hand (that is relatively inexpensive) and fit a new hand to correctly interface with the ratchet teeth. After all, they do want to keep you as a happy customer, and if the “fixing” doesn’t get too involved it’s a good public relations move.
I would hope that by now you might be questioning the actual knowledge and skill that your friend really has. It appears to me that he has addressed everything except what really needs to be corrected. Working on the ratchet teeth takes skill and experience, and mistakes are easy to make.
Smith & Wesson does not make a selection of extra-long or wide hands. At one time they made an extra-thick hand so that the timing could be corrected in a revolver that had a worn hand slot. While I’m not sure if they still make them or not, I don’t believe they offer them for sale as a spare part. In any case one of the older hands wouldn’t work in your new model 27.
It’s up to you of course, but given what the gun cost, and the potential of amateur fiddling and fooling around that has been described so far to make things worse; I would return the gun to S&W even if I had to pay for the work, and charge the expense off as a learning experience.