Adjustable or rider-controlled trim tabs, IHRA

IHRA answers this part for 29 of its classes. 0 of those answers permit the part outright and 9 permit it with stated conditions, leaving 20 that do not. 3 of the ones that do not are classes we read as open rather than as refusing it. 20 are inferred from how the class is written rather than quoted from a rule naming this part.

Where it stands, class by class

29 classes, grouped where the same rule gives the same answer rather than listed one by one, because an answer that holds for a class usually holds for every class that borrows its rules.

What each answer below means

Not permitted, not listed in the rules: Treat it as coming off. The class requires the craft to stay stock except where the rules allow otherwise, and this part is not on the list, so this is our reading rather than a rule we can quote at you.
Legal, with conditions: Keep it, but measure it: the rules permit this part only inside stated limits.
No rule, this is an open class: Probably keep it. The class carries no stock clause at all, so anything unlisted appears to be open. The rulebook does not say so in terms, and this is our reading rather than a permission anybody wrote down.

Not permitted, not listed in the rules 17 classes

On a closed list an unlisted modification is not permitted. · A.2.2, J.1

Legal, with conditions 2 classes

Aftermarket FIXED-POSITION only. Limits: max extension 100 mm.

Ski 1100 Modified · R.5.2
Ski 1500 Modified · Q.5.2