As Ron stated, as long as you have isolated transformer output windings, the regulator doesn't care which output is grounded.
Many years ago I made a dual bench supply in that way (which I still use) with a transformer that has dual isolated output windings. I can then ground the outputs as I choose, either to get a plus and minus supply, or connect them in parallel to get double the output current at a single voltage (the outputs have adjustable current limits to help balance the load when they are paralleled).