I'd want to be able to use something like that from a dialog. And if possible, without extra file editing. The eff file format scares me, and i've not used it because of that. Since i want to do something complex (incrementally adding 'stats', from calculations derived from locals/globals), i'm not at all sure if i can do it efficiently.
For instance, i assume that adding 1+ creature effects might eventually slow down the game or lead to bad things, if there are hundreds of these little increments. Ideally it would be possible for me to 'remove the old' and 'add the new, accumulated', so a sort of ID would be nice (or at least, that eff on a single stat are merged or something).
This is also a obvious problem for 'percentage modifiers'. I assume the engine has a defined, sorted order in which it applies things.