Balderdash!!
Warnings against doing anything to a Glock is standard procedure, whether uttered in print form, or from the mouth of one of their employees, techs, or armorers. The "Standard Product Liability Warning" was developed by manufacturers for one reason only, to legally help them remain free from liability...ANY liability. It doesn't mean that anything you do to the contrary would be bad for you...it means that it could potentially be bad...for them!!
The careful and correct polishing of where intermingling parts intermingle with each other can accomplish a better surface to surface condition than the 1,000 round trigger job, without actually firing 1,000 rounds. This better/smoother/polished surface finish between interacting parts reduces the friction between them, and less friction equates to the reduction of the energy required to motivate said parts or mechanisms.
The 0.25¢ trigger job will in no way create a hair trigger - only a drastic change in geometry can physically accomplish this.
Polishing will also in no way degrade a material's qualities of stength, in fact, removing the sharp edge(s) of sheared or stamped metal (i.e., as found on a stamped sheetmetal Glock connector) via radiusing or polishing will decrease the chances of fractures that would normally originate at these sharp edges, if some strange outside force that was not originally anticipated by the manufacturer was placed upon it. I don't see that happening inside a Glock pistol.
I'd be more worried about those who swap out their connector, trigger group, magazine release, recoil assembly, slide & internals slide parts, i.e., swapping out the OEM parts for a titanium striker, safety plunger, etc., before they've even shot a single round out of the pistol, then come here looking for answers about why their Glock doesn't function as designed!