B.R.
My suggestion would be to introduce the item you want to make at a regular dinner. If it is to die for (for example if you are good at making homade crescents) then they will be more accepting if you offer to make it for holiday dinner or may even request it. BTW what it that other food item? As far as how traditions work, I know how you feel; I lived with my inlaws for five years. I love to cook and they found this out quickley as they got to sample my food; soon my recipes were being requested specifically for birthdays and holiday meals.