If by "saved changes" you mean you saved the project file, then yes you can easily reset an fx used in an event.

In the fx pop-up window, you see a box with the name of each fx filter you have applied, in a horizontal display across the top of the window. This is called the fx chain, the order shown is the order in which the effects are applied. You can select one by clicking on it. You can delete it by clicking the little box near the upper right that has an X over it to indicate delete. Then click the little box to its left to open the fx selector and reselect the one you deleted. Some effects differ depending on the order in which they are applied, if you need your newly added effect to be in the same place as the one you deleted, you can just drag it to the location in the chain where you want it.

If you mean you clicked OK and applied the non-real time effects:
I believe the non-real time effects don't actually modify your event but rather create a new event over it in the form of a take. The take has had the effects applied to it so you can not undo them. But you should be able to start over by selecting the original take and starting the process over. This will create yet another take.