To create a custom set of parameter labels, from the View tab, select Parameter Labels, and then click on Modify Labels. The diagram below shows that we have created the set called "New Parameter Labels" with 4 custom-named parameters. The template file used may be selected or changed by clicking the ... (ellipsis) button to the right of the Template File: field.

Set custom labels for one or all of your parameters by clicking on the Add button and selecting the parameter to modify from the drop-down menu. Enter the new name for the parameter selected. Once you have created your set of customer parameter labels,  click OK to close the Parameter Labels window.

Once you have created your set of custom parameter labels, you can now select to use them on your plots.  Access the Format window by double-clicking the plot. Under the Axis category in the window below, click the radio button next to Parameter label set and select the set you want to use from the Parameter Label Set drop-down menu in the Derive Axis Titles from section. In this window, you can also change the text formatting (bold, italic, font, size, color, etc.) of the parameter labels (options not shown).

Below is a plot before the parameter labels were changed (left) and then after (middle and right)

Importantly, parameter label sets do not change your original data. The plots uses the set you defined instead of the parameter labels in the data file.