In this instance I don't believe Experiments would be suited as they are mostly used for varying facilities such as Virtual Goods, Messages, Achievements and Leaderboards.
In this case I recommend making use of Segments to divide your players up and, using a Segment Query, differentiate the return of the event in Cloud Code.
Our tutorial on Segments can be found here, and we have a range of Segment-based tutorials here.
We have event that return a value from database(values stored in runtime table) to player at login.
I would like to create experiment that segments the event so i can return a different value to different players and this value would return to default one after the experiment.
Is it possible to segment the event or do i need to include tests in the event to see if player is in the experiment and witch percentile?