The Rule is:

You may Purchase, and Maintain, One personal plot of land, and One free company with a plot of land, per World, per service account.

How can you not understand this?

If you have a second character, on your service account, that is in an FC and the Master goes away long enough for leadership to change and it by chance goes to your second character, and this happens to be on the same World as your Main that has a house with an FC, then you are breaking the Rule by their definition.

Will they do anything about it? I doubt it.

Its a Rule to follow, whether or not you do so is up to you, but just be mindful they could act on it sometime.

That is all there is to it, best to not deliberately test if they will, I'm pretty sure that in the case of you being made Master of a second FC by the system would not result in some form of punishment, the system should know that you already have another FC already with another character and thus not even allow it, but this is SE, they don't think it through.

If you on purpose buy or create another FC with the intent on getting another plot, then its fair game if they catch you out.