1. There are a couple of notes here on how you're doing the analysis. First, you are calculating the flow by first getting the normal, then the normal component of the velocity, and finally integrating over the clip. All of these steps can be done by using the Flow() calculator function. If you use this function, indeed, it will do exactly the steps you are now doing manually. Give a looks at the User Manual, ch. 7.3 for a description of Flow()
Now, about your question on how to not-overwrite the variables. This is possible in 10.1.6 (and prior), but it is easier to do with the latest version, 10.2.
If you're using EnSight 10.2, you will see that it contains a new kind of variable: Constant per part. This is a variable that return a single value for each part it is calculated on. So, if you select all your clips, calculate Flow() on them and set the output to be Constant per part, you now have the Flow() variable that, for each clip, returns a single value the flow of that clip.
You can right-click on the Flow variable on the variable list (bottom-left) -> Plot vs. Time. This will create the plot with all the queries of Flow vs. time, for all the clip parts.
Now, you want to export the queries as single .csv file. Simply right-click on Flow in the variable list -> Export constant to csv
2. If you need to get the values of the plane tool used to create a plane clip, use the following commands:
from ensight.objs import core
core.PARTS[i] will be the part corresponding to the clip plane part - set "i" to be the correct index. This will return the three points that are used to define the plane tool. From these points, you should be able to extract origin and normal of the plane tool.
Let us know if you have questions or need more help.