"have had to modify UAnimNotifyState_TimedParticleEffect in order to subclass it. I added 'ENGINE_API' and removed 'MinimalAPI'. I also needed to move 'ValidateParameters' from 'private' to 'protected' in order to implement a custom NotifyBegin.
Would you be willing to take these couple simple changes to elimate an engine modifcation for us?"
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-68917 in the post.