Here is my opinion, based on experience - do not use the import site list function. It works just fine, but it could cause issues later. Over time many links go bad, and they sit in your verified list until you clean them through one of several means in the SER software (Reverify, Cleanup, etc).
Here is the problem with using the import site list function - if some of the links in the verified site list are bad (and they will be), you can't build a link to them. Furthermore, you can't purge them from your verified list since you never built a link with it, a requirement for any cleanup. Over time, your verified list will accumulate more bad links. If you delete projects, and those links go bad, they will pollute your verified list as well. If you are running off of your Verified site list, bad links will kill your LPM. I get over 100 LPM with a clean list, and under 20 with a dirty list.
Here is my recommended way to import a sitelist:
1. Save the new sitelist to its own folder (duh)
2. In Global Options=>Advanced, point your "Submitted" folder via the dropdown menu at your new sitelist. Be sure the "submitted" box remains unchecked when you are done. Otherwise, you will pollute your nice new list.
3. Make sure the "verified" box is checked.
4. In your projects, click the checkbox "On" for options=>submitted (under the search engine selections). Identified, Verified and Failed should be unchecked.
5. Uncheck all of your search engines. You only want to run off of your list.
Start SER and run it until your LPM collapses. You will be amazed at your LPM. When your LPM finally dies, go back and undo the steps above.
SER will read and build links from your submitted list (your new list), and save them to your standard verified list.