The “why not” is because everything happens with each stroke of the handle with a progressive press. You can “shotgun” try and solve changing all sorts of stuff and get lost. It’s actually pretty easy to get lost in all the things you don’t know, being new to a particular progressive press. It is for this reason alone, I suggest one use any press as the mfg. designed and shipped as is for at least enough time as it takes to see how it works as intended. If you have problems and contact the people that designed and built it, they will know exactly what you are working with, if you don’t alter it before hand. More importantly you will know from first hand experience if any change from the factory configuration you make, is an improvement or not. If you “fix” something you have never used, you won’t know if you made it better or worse.
Think of progressive as doing one thing after another (because that is what you are doing), to the point all are completed at once.
So, set station #1 up. Once all is right on #1, move on to #2, then #3, and so on. It would be unsound reasoning to think you can repair unacceptable results from a previous operation, in subsequent steps.
If you can’t seat a primer correctly, there is very little reason to move on. A fail at #2 but making something after that better, doesn’t make the end product work as that goal has already been lost. Focus on the issue at hand and solve it first, after that you can address other issues that may or may not pop up.
I have tried all sorts of stuff because I enjoy learning something I didn’t know. MANY of the folklore “upgrades” on the 650 might be beneficial for a or a few specific conditions but are not “game changers”.
Chopped up springs, bearings made from different materials etc, are sold from a number of places. If you want you can try them all yourself but a thrust washer and two flat shims will beat them all.
On the 650 the Timken 815-NTA is the one you would use and is less than $2.
https://www.zoro.com/tritan-needle-thrust-brg-bore-0500in-18300-rpm-nta815/i/G0317759/feature-product?utm_source=google&utm_medium=surfaces&utm_campaign=shopping feed&utm_content=free google shopping clicks&gclid=Cj0KCQiAmpyRBhC-ARIsABs2EApprY2ygJMhtEXVxNLN3iOY7TLJBE0wI7hZQY4ZLkHUggcYNd3XbNUaAvP0EALw_wcB
As far as 650 modifications go, the thrust bearing can be beneficial and the 3D printed primer system “switch” is nice.
I would put both well above ball/spring alterations under the shell plate.