The original question had to do with finding specific rules governing the allowed uses of displaced threshold runway surface in various countries, If I understood the question correctly. In the USA, I am unaware of any specific regulation on this subject. However, the AIM guidance on runways and their markings indicate that the runway area prior to the threshold markings (displaced threshold marked by arrows) is not available for landing touchdown, even though it is available for takeoff, taxi and rollout. FAA actions against pilots sometimes cite the pilot's disregard of the AIM guidance on an issue as evidence of a FAR 91.13 "Careless or wreckless" violation even though the FAA officially refer to the AIM as "non-regulatory guidance" or "advisory in nature". In other words, you may not be legally required to follow this "advise", but if something goes wrong....
Runway thresholds may be displaced for any of a variety of reasons other than obstacle clearance plane considerations. These include, but are not limited to, ILS navigation signal integrety requirements, pavement structural strength requirements or even airport neighbor concerns about low flying aircraft and noise. One southern California municipal airport with a stong anti-airport contigient proposed displacing the runway threshold to discourage it's use by jet operators. So far, FAA does not support this course of action.
Under FAA regulations, large and turbine powered aircraft must maintain at or above any electronic or visual glidepath guidance while approaching the runway and may not descend below this path until necessary for safe landing. Vertical guidance is typically aligned so as to provide for a threshold crossing hieght of 50'. Glideslope angle may be raised above the standard 3 deg. and/or the threshold may be displaced to provide required obstacle clearance. On shorter runways, contaminated runways or with adverse wind components, It may sometimes require that vertical flight path angle and aim points be adjusted in order to intersect the runway surface at an acceptable rate of closure at the required touch down point for the situation. These adjustments must still allow conformity with applicable stabilized approach requirements and safe obstacle clearance. Under these conditions, firm touchdowns and maximum allowable braking may be required. Aiming shorter to land sooner or touch down softer IS commonly done by many pilots but it must be understood that there is little defense if something goes wrong. In low visibility conditions or at unfamiliar fields, especially at night, many accidents have been traced to pilots succumbing to visual illusion and hitting obstacles. Intentionally landing short of the threshold marking is not normally viewed as acceptable except in the most extraordinary circumstances of emergency. Normal approach profiles intersect the runway surface at aproximately 700-1000' beyond the threshold marking depending on the specific descent angle. Roundout places the touchdown point somewhere beyond this. The higher above and further forward the pilot sits relative to the main wheels at threshold crossing attitude, the closer to the threshold the mains will touch and the closer the aircraft will pass to any ground obstacle in the flight path.
I realize that the above is not all clear, black letter law, but I hope it is helpful anyway.
Best regards,
Westhawk