A user of fuel must utilise an accepted standard of fuel if they are to avoid engine damage or excessive wear. And importantly, not invalidate their engine manufacturer’s warranty.
Consequently, without a certified ‘Letter of No Objection’ from any engine’s particular manufacturer (basically giving permission to use a non-standard fuel), they cannot use a fuel which does not conform to an accepted Standard or a fuel whose formula has been altered or contaminated. The addition of chemical formulas to any fuel (like adding Fuel Conditioner) could then classify that fuel as non-standard or contaminated.
However, if the lubricity and combustion performance of a fuel with added Conditioner remains within the strict parameters of EN590, then it is considered a Standard Fuel and cannot legally breach the terms and conditions of a manufacturer’s engine warranty. This negates the need for obtaining ‘Letters of No Objection’ which are almost impossible to obtain.