You shouldn't cause an issue if you select the wrong type as there's no real difference when dealing with an existing preview build as the settings from that will be maintained & all of the builds essentially act like they're portable installs anyway

Also if it's in the Program Files folder then it's likely to be non-portable install.
You can however check by looking in the paths.ini via a text editor within the root of the WACUP program folder to see if there's a
portable=1 line in there or not. If it's set to that then it's deemed to be a portable install.
-dro