No, it cannot be I wish I resigned.
The first sentence refers to an action that had been done.
A man resigned before one week, and feels sorry about it now.
So he says
' I wish I hadn't resigned'.
Let us now take a look at the second sentence.
I wish I resigned. This expresses one's thought that he wants to resign.
For example, your friends were terminated from a company, but you were asked to continue.
You feel a lot about the loss of your friends and you say, 'I wish I resigned'.
How is it?
Sooris