There is a white nylon, delryn or teflon spool bushing rather than a bearing, inside the reel behind the star drag. Can this be replaced with a ball bearing?
It could, but it won't do any good and will actually slow the spool down. The spool is suported in 2 other places. The bushing you are refering to is only there to provide lateral support to keep the spool shaft from bending under excessive tension. The inside of that bushing is bigger than the spool shaft. Take the cap off and spin the spool. You will see that the spool shaft doesn't touch the insides of the bushing.