Many OTS builders feel that ANY substitution or change from the plan degrades the spirit of the event. The OTS model should be built exactly as shown on the plan, warts and all; "bouncy" landing, and all.
There is sometimes a temptation to fudge here and there in hopes of making a better flyer out of one that maybe wasn't so great, after all.
Sometimes, substitutions are necessary. This usually applies to wheels, props, spinners, which are no longer available. OTS officials understand this difficulty.
Any design change is looked upon with great suspicion.