This demand letter may become evidence in a future case and judges don't look kindly upon lies and deception.
You definitely don't need to cite the legal justification for every demand you make in a demand letter.
You don't even need to have a valid justification to make a demand in a demand letter... it is common and normal to make arbitrary demands... they are negotiations.
https://www.wipo.int/en/web/trade-secrets#systems
Now yes, they're fair game for reverse engineering, but that doesn't mean someone can't be mad about it and tell you not to do it.