The Fundamental Principle of Laser Racing
'No changes to the boat are allowed unless specifically permitted by the Class Rules.'
This principle underpins the Laser Class Rules. In most classes, the Rules work on the principle that unless something is forbidden, it's allowed. This can allow you considerable latitude to experiment with your rigging. Unless the Laser rules say you can alter something on a Laser, you can't.
Most 'measurement' in the Laser Class consists of scrutineering, a check that you have set the boat up to comply with the Class Rules. Most errors come from insufficient knowledge of the Laser rules, not from deliberate intention to gain an unfair advantage.
The Measurer's aim is to help you make sure your boat is rigged correctly, not to catch you out. In almost all cases you will be given ample opportunity to make the change before you go racing. With universally interchangeable Laser parts, last-minute changes are usually easy. (The exception would be if you have arrived at an event with a 'replica' sail or 'replica' spars, and even then we'd probably try to help you sort something out temporarily.)
In some classes, Measurement is about measuring whether your sails and hull fit the class rules dimensions, and that the hull weighs no less than a cetain amount; how you rig the boat is up to you. In the Laser, because the way you rig your Laser is a crucial part of the Class Rules. You can be scrutinized at any time during a regatta. A Laser Measurement Certificate (that is, if Laser still issues them) is without any value for measurement purposes, which means that it has no value at all.
In the UK there will be a greater emphasis on providing measurement support at UKLA-run events, with experienced sailors available to advise you about the Laser Rules.