Hi,
Data sources won't move to cusotm package.
You will repalce $tmp with Custom package.
You need to select proper object type at SE03 R3TR RSDS-->click on change object directy entry, there you will see $TMP editable screen.
Have you created custom package?
Can you share screen shots which you done.
Mean while please search on google and find clear steps.
google search word as "changing the packages sap technical".
Thanks