A quick search brings a few possibilities:

"I rotate it in a photo editor such as Photoshop"

"You can rotate the texture in Poser by swapping the U and V" on the material. But that means 90 degrees each time.

The Poser Forum at Daz has a 2013 "Rotate texture map, how to" thread with lots of details and a node screenshot for doing this:

"You can get the U, V values from the Variable 'brick' which you could transform using basic trigonometric functions - for a rotation angle A you'd replace u with U * Cosine A + V * sine A."

Looks like you could get a precise angle with that Poser node setup.

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