build/transaction_envelope.go
func (b *TransactionEnvelopeBuilder) MutateTX(muts ...TransactionMutator) {
	b.Init()

	if b.Err != nil {
		return
	}

	b.child.Mutate(muts...)
	b.Err = b.child.Err
}
func (b *TransactionEnvelopeBuilder) MutateTX(muts ...TransactionMutator) {
	b.Init()

	if b.Err != nil {
		return
	}

	b.child.Mutate(muts...)
	b.Err = b.child.Err
}
// MutateTX runs Mutate on the underlying transaction using the provided
// mutators.