Ok, try selecting the Niagara component in the components panel inside of your BP, then changing the setting there should spawn all instances of the BP with the setting on.
OR If for some reason that does not work, you could try to explicitly enable it. (Firing that logic on BeginPlay could work too, but the construction script happens just a little bit sooner)
For the record - I tried this with the ‘MeshRotation_System’ in the content examples (Incase you are using something different than a mesh renderer and still having issues)
Tangentially related: If you select a variable in your BP you can enable ‘expose on spawn’ and that will give you those inputs on your ‘spawn actor’ node.