Yes you can use a Prompt to name the source column, but it requires modifying the underlying code.
Are you sure you need to modify the Source column name, or do you need to choose the source transpose variable from a list?
If so create a Variable Prompt and add as below
If you really need to modify the Source column name:
1) Create a Text Prompt, with the list of values
2) Add the Text Prompt as in your example under Options. Run the task.
3) Start typing in the generated Code to create a copy
4) Right-Click on the code under the Project tree on the left to modify the code properties. Select Prompts, add the Text Prompt.
5) Modify the PROC TRANPOSE, NAME= option as follows:
change NAME='&prompt_2'n to NAME=&prompt_2