Not sure how to do this, since I don't know what spells people are going to want by default. Or how in general to deal with things people might want to override.

I think the right answer is probably an [options] condition. The the default action list can be

PreCast [options:precast] ...

After that it would be better to change CopyTargetsMount to work the same way, but that is quite an incompatible change for people who have already edited their action lists.

Since the advent of rules this is clearly a case where a rule is the right approach.

Added in the feature_newargs work. Closing.