Yes.
To split the contents of a portfolio, load it into EstateVal, GiftVal or CostBasis, then use File → Save As... to save it as the name of the first of the two new portfolios. Next, select File → Save As... again and save it as the second. You’ll now have three copies of the original portfolio, with three different filenames.
Now, load the first of the new portfolios into the program and simply delete all the lots that do not belong to it anymore. (You can delete a lot from the grid with Edit → Delete Row or Ctrl+D, and you can move lots around with Edit → Shift Row Up and Edit → Shift Row Down, or Ctrl+Up and Ctrl+Down.) Any existing evaluation data will be preserved, so you won’t be charged for generating new reports with the reduced number of lots. You can also change the title or account information to reflect the contents of the new, smaller portfolio, and then generate the report you’re interested in.
Finally, load the second of the new portfolios and repeat the deletion process, but this time with the lots you preserved in the first. Again, you can change the title or account to reflect these changes, and any evaluation date is still part of the new, reduced portfolio. Regenerate the report.
You now have your portfolio broken up across two new files (with the original preserved as back-up), and two new reports that reflect the split.