Official trails built with permission, then should only be modified / maintained by the trail builders/team. But then that would be in trail centres etc.
Anything else is trail evolution. If they build crap, just change it again.
Still waiting for the obsession with gap jumps to die down in Surrey Hills. At present it seems every trail, even if it was a nice flowing swoopy fast trail suitable for all, needs an awesome wicked big gap jump right in the main line, and fill it with sharp pointy things, then leave the spoil on the side where you could have at least done a chicken run. 🙄
Problem is the crap and especially dangerous changes may get the landowner to demolish it all.
Sometimes it’s good though. Talking to some trail builders who did some stuff years ago they’re pleased that people have taken the trails to new levels.