I don't think this is accurate. You can remove pre travel the same way you remove over travel. There is no visible outside modification. As long as the safety tab engages then i don't see removing pre travel a problem.
In most cases people want to remove a lot of take up, for the most benefit, just to where the trigger comes back out at reset and stops, therefore needing to trim the safety tab so it will still engage. By doing those 2 things the rules have been broken because now the trigger looks different than stock configuration because it sits further back than stock, and the safety has been trimmed.