I've been asked to make a cake using the yellow cake box mix (I've never tasted it). I use box and extender normally for baking.

I worry that if I use the extender recipe it will change the taste of box mix, how do I avoid this? I should I just go with box mix and no extender? TIA

Yellow cake mix is one of the few that I will eat, it tastes good, especially the one using melted butter in the recipe

I've used extenders before and I do think that it changes the flavor just a little bit and makes the cake more dense. If the customer likes the taste and texture of the yellow cake mix then I would use it as is without the extender (so it's like the way they're used to). If you need to carve the finished cake then I would tell the customer that to make the cake more dense you need to add additional ingredients and that it might change the taste slightly (better to forewarn then to have them surprised when they bite into it).