I noticed when I display a UV map that is square and try to change it to a rectangle that it stretches out the islands to 200% in the direction of expansion. Is there something I am missing to keep the islands at current shape. I fix this issue by selecting all the islands and scaling it by 50% in one direction, but I was wondering if there's a way just to do this without having to take the additional scale step.

Could you make a screenshot and provide steps, what you expect to get and what you receive?

To answer your question directly: yes, stretching UV islands disproportionately is unavoidable when switching a texture from square to rectangular. This happens because regardless of its aspect ratio, a texture always occupies coordinates from 0 to 1. When you select a rectangular texture, you don’t change the actual coordinates, but rather how they are displayed in the UV Editor. The main UV tile still ranges from 0 to 1 on both axes, even though it now looks rectangular. This is exactly why your islands stretched — they simply preserved their original coordinates. To fix this, you need to scale the UV islands back in the opposite direction by an amount based on your texture's aspect ratio. To avoid this issue in the future, simply assign the rectangular texture in the UV Editor before unwrapping or creating your islands. This way, the tools will already recognize the rectangular proportions and calculate everything correctly from the start.

Well that makes sense. I'm just not used to working with non-square textures. Not in last 10 years anyway. I don't recall ever having this issue when I was in 3D Studio Max but I gravitated away from Max a long time ago. So it may be that that was just so much in my workflow that I didn't even think about it back then. Thank you for your answer