In Pt, level 100 Pokemon can't gain EVs, so you need to EV train before that. The best answer I know for your second question is
1. save the game
2. feed it the EV berry that lowers the stat you want to measure
3. count the number of EV berries you need to decrease it to 0 (note that any stat with over 100 EVs will be lowered to 100 EVs when the Pokemon eats one berry)
4. reboot the game
If that's not good enough, then I guess you need to assume it's screwed up, feed it EV berries until it has no EVs in that stat, and redo your training for that stat. However, if you happen to have access to a screwdriver, then such screwups should be easier to unscrew.
(read those next time you have a question about EVs)
Additionally, EV training goes a lot faster with Poke radar, so you might want to try learning how to use that.