There have been a number of requests for a way to make Liquid use Linear interpolation rather than Bezier interpolation for the RT effects editors. Here's a way accomplish this.

Double click on a RT effect editor in the library (for example the 2D Editor CPU effect). This will open the effects editor with the default A and B "V" image in the monitor. Collapse all of the parameter blocks and then expand a parameter block for which you want to use Linear interpolation by default. The reason for collapsing all of the panels is to simply the keyframe graph. Let's say you want to make the position use Linear by default. Expand the Position block. This will display the X and Y position lines in the graph. Because they both start at 0, you can't select both lines in the graph. Change the X and Y positions to different values so that you can see the separate lines. Right-click each line and choose Interpolation->Linear. Set the values back to 0. Close this parameter bock and repeat for each other parameter you want to change.

Now click on Exit. This will pop up a question asking if you want to save the edited effect in your project. Choose Yes. This will place the effect in your bin under the New FX rack. I suggest renaming the effects in this rack to reflect the changes (e.g. 2D Editor CPU - Linear). When you want to use linear by default, drag this effect to your clip instead of the one in the library.

Hope this helps.