Is there a way to mirror landscapes 45 degrees? Mirroring outside of X/Y?

Development World Creation
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1

In the editor, you can mirror along X, Y, or rotate about those axis.

But I want to know if I can rotate around other custom lines of symmetry.

For example, in the image, I can rotate along the green line (or perpendicular). But I want to mirror along the blue line (a 45 degree rotation of one of the existing mirror lines.

Is this possible? If not, is there a work around?

Thanks!