While this forum is all things VEX, it’s mostly around the VEXIQ and VEX EDR line. Your question is about VEX PRO parts.
I’m assuming you are talking about this part https://www.vexrobotics.com/217-6293.html which is the versa 90 degree adaptor. If you are talking about that part, look at the video on that page, there is an adaptor that goes onto one of the gears and lets you mount another shaft on that to let you gang the adaptors or feed into another one of them.
You might want to post on https://www.chiefdelphi.com/ and ask there. That forum is for FIRST FRC roboteers and they are heavy users of the VEX PRO line. They would be able to tell you if a stock 90 could support a thru shaft or what modifications you would need to make.
My only experience with the adaptor was a short shaft in from the Planetary and then a right hand turn to the sprocket that was chain driving the rear wheels. ( an attempt to power a 3 wheel delivery trike)
Pretty sure it is made to drive into your VP gearbox. I suspect it would be advised against to mount it at the output stage because the VP boxes are better placed to handle the shock loads at that end of things than the bevel gears would be.
But either way, I don’t think you can pass a shaft through any way.
It’s a trade off, do you want the high speed at the 90 or the high torque at the 90. My application was like @zeus, motor, planetary, 90, chain sprocket. The sprocket shaft was held at one end by the 90, the othe by a support bearing. So far, solid as a rock and it’s dragging the bike and me around pretty well.
The VEX PRO line is pretty indestructible if you follow their guides.