You can set negative values for Spell fields in the Object Editor and get the reverse effects in a lot of cases. In the World Editor, go to File/Preferences/General and turn on "Allow negative real values in the Object Editor".
So take Cripple for example, which reduces Attack Rate, Movement Speed, and Damage. You can set it's values to negative values which will then INCREASE Attack Rate, Movement Speed, and Damage.
I attached a map with two example abilities using the method I explained above. One is a Targeted ability and the other is an Instant ability that both do the same thing, increase the unit's Attack Rate and Movement Speed.
-The Targeted ability is based on Cripple with negative values.
-The Instant ability is based on Fan of Knives (I removed the damage from it). It uses a trigger that creates a Dummy unit (a completely invisible and uncontrollable unit) that casts the Targeted ability (Cripple) on our casting unit. This is a very simple trigger so you shouldn't have to worry about any bugs or issues.
And Cast Animation is a little vague. I'm assuming you want to reduce the Cast Backswing and Cast Point time? You would have to use triggers in order to do that.
1) First you would have to keep track of each unit's default Cast Backswing/Point durations.
2) Then you would have to detect when your unit receives the Spell buff
3) Then you would have to adjust the Backswing/Point using the new natives (decrease them)
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Note: I'm not sure if these work yet. A lot of new Natives added in the recent patches don't work yet.
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Unit - Set Unit: (Target unit of ability being cast)'s Real Field: Animation - Cast Backswing ('ucbs') to Value: 0.00
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Unit - Set Unit: (Target unit of ability being cast)'s Real Field: Animation - Cast Point ('ucpt') to Value: 0.00
4) And finally you would have to detect when the buff ends/is dispelled and adjust these two values again (increase them)
