Creating a mogrt in HD and 4k with two different frames. 30 and 60 in one project?

The only reason to create two different MOGRTs is if you want different levels of motion blur. Keyframes are based on time, and the frame rate does not change timing. The only way to change the timing is to use an expression that counts frames instead of time. 

If you have footage shot at 60 fps (59.97) and a 180º shutter, the motion blur will be half that of footage shot at 30 (29.97) with a 180º shutter (standard exposure time is equal to 1 over 360 divided by the shutter angle multiplied by the frame rate - 180º shutter at 30 fps = 1/60 second exposure time).

If you wanted to get fancy and have one MOGRT that would work with any frame rate and still match the motion blur, you could apply Pixel Motion Blur or CC Force Motion Blur on an adjustment layer and add the Shutter Angle to the MOGRT (or use a slider and some math), then create one MOGRT at the Maximum frame rate you expect to be using. I created a few MOGRTS at 120 FPS with Shutter Angle Controls, so I can use them in any Premiere Pro sequence and match the motion blur or even exaggerate it. I also have created many MOGRTs for clients with Menu Options to change the size from 4K to HD, to Social Media Square, to Social Media Landscape, so they only need one for any frame rate or frame size project they are working on. All it takes is a few simple expressions and some protected areas. 

I cannot imagine a MOGRT scenario requiring me to create an identical animation at 30 and 60 fps when one at 60 with Pixel Motion Blur (my favorite) added would do the job. 

Due to the way they are loaded in Premiere based on the saved file it is preferable to have them separate. Especially if different framerates are involved and/ or there are linked parameters for Essential Graphics things could get confusing not just for the user but also the program like messing up expressions when the controls have the same name.

Mylenium