These devices can be made in either polarity. Some conduct from Drain to Source, and others go the other way round.

Given the way this one was wired originally, (+) connects to the Drain pin, and (-) goes from the Source pin. The modified circuit doesn't change that (in theory).

It should all still have exactly the same voltage drop between Source and Drain as it had before, but now there is going to be a different voltage between Gate and Drain than what was there before. I don't know if/how that changes anything.