The emulsion is identical between the normal RC and the Portfolio RC, so the base will not make any difference with respect to your image. If you look at the numbers for the ISO range and speed (
https://www.ilfordphoto.com/amfile/file/download/file/1956/product/2019/) you'll see they're identical, and the characteristic curves are the same too.
So yeah, no problem at all doing tests on SW until you're ready to pull the final print.
This approach also works with different emulsions, as long as you know what you're doing. I use the Kentmere RC to do all my test prints, and when I'm ready to print, I use Ilford FB with minimal adjustements. Both have very similar ISO R and P over the range I am working, and I need maybe a 1/4 stop adjustment in exposure to match prints.