when I change the font, I lose the effect and have to start all over again
That does not reproduce as @Hudson555x shows.
Can this be separated so changing the effect does NOT reset the font?
However, currently presets store all parameters such that choosing one overrides anything you have done. This could be changed fairly easily for the stock presets that only describe certain things like motion animation. The add custom preset UI could be changed to show a list of checkboxes of which parameters should be saved with the preset. These are not trivial changes but also not very big. It is a good suggestion, and I hope we can do it by the end of the year but not promising.
In the meantime, user-defined presets can be modified as they are text files if you can figure out which internal name maps to the parameter name that appears in the UI. The same cannot be done for stock presets.