In the absence of written rules, you can in theory do what you want. (And others are also free not to follow you, and to keep using Pelecaniformes, Gruiformes and Apodiformes.
)
Still : note that, if rules were to be written, I can easily imagine that something equivalent to
Art. 35.5 (for family-group names) might be included to protect established usage.
Pelecaniformes, Gruiformes and Apodiformes have been traditionally used at the rank of order, while Ardeae (now 'Ardei'), Ralli and Trochili have traditionally been used at the rank of suborder (within Ciconiiformes, Gruiformes and Apodiformes, respectively). A 35.5-like rule would give precedence to the names traditionally used at the higher rank, whatever their date of availability.