Excellent-- yeah, the blur2d function explicitly looks for just one function named “XY”, and combining the functionality is a good and simple way to deal with it.
An alternative would be to clone the blur2d code out of the library and into your sketch, making blur2d_shades or whatever. But your way works great and is far more maintainable!
Thanks for helping put my mind at ease, and also highlighting a confusing point that probably needs some explaining.