Would it ok to turn my onwall VP150 vertical behind an audio transparent screen?

Dave, welcome. Some time ago Alan Lofft experimented with using VP150s vertically as main speakers. He reported that the results were quite favorable. Positioning your on-wall VP150 vertically should be, if anything, better than the horizontal orientation.

Generally, it's not a good idea to change the orientation of a speaker (here come the jokes), but there are exceptions.

Best to simply try it temporarily and see how it works for you!

No harm in experimenting!

You mean those camps aren't for real?

Horizontal speakers are a compromise from the get-go. Placing the cabinet so the driver complement is in a vertical array can be beneficial to its dispersion and overall timbre but NOT the other way around (vertically designed driver complement placed in a horizontal array).

::snicker::

I saw that coming... Especially after the orientation comment

Sadly, they are, but the orientation almost always seems to revert to the original state after a while ...