Psynapse thanks dude, but I found a quicker way:
Copy and paste all the required keyframes.
Go to the Scale opt. in the graph editor and choose in the Time Range: Start/End and also in the Method.
In the Time range area enter the frames (examp: 1 and 10) and in the method area enter the last frame first and the first frame last...(examp:10 and 1).
That should do the trick! : )
btw make sure to tick "Only Scale Specific Keys".