I have found one way to save a curve preset BUT it is not perfect
make your curve preset
then make a shape (or a word)
Nest the preset in the shape
Save as an asset
To use the preset
drag the shape from the assets and un-nest the preset
drag the preset to wherever you need it
finally, delete the shape.
In this zip i have made a weird curve preset -saved as an asset
see if it works for you
It isn't perfect but its the best i can do.