Once you have purchased a product (albeit a different version) you will not be offered the trial version to install.
You should be able to work around this by logging out of your account on the Reallusion Hub and then create a new RL account using a different email address. Then if you sign into the Hub with the new account details you should see the trial versions listed. However, please be aware that you will likely need to uninstall your Pro version to be able to install the Pipeline version.
As you probably know, the only real difference between 3DXchange 7 Pro and Pipeline is the ability to export to FBX and BVH formats from both iClone and 3DXchange.
Peter
Forum Administrator
www.reallusion.com