There is a method, I forget the exact name, something like "make_action_orders". Here is where the order is determined for this entire turn.
It will cause issues. Believe it or not, I know what I'm doing when it comes to scripting. Here's an example, lets say with 2 enemies and 3 party members.
1. Method is called to create order that battlers choose their commands.
2. The order is: [Enemy1, Party2, Party3, Enemy2, Party1]
3. Oh, look! A bug already! How does Enemy1 know if there will be a party member whose going to use a basic attack?
4. He can't.
5. So we have two options to have him take. Lets follow the first option:
Option 1
1. Enemy1 chooses to use a basic attack anyway, he assumes somebody will use a basic attack.
2. Here we have two possibilities:
a. A party member chooses to attack and the turn executes flawlessly.
b. Nobody attacks and he is stuck with nothing to do, since his attack is based off a party member attacking.
This can be exploited by the player to practically be invincible.
This is assuming we have modified how he targets and the game hasn't crashed already.
I can think of numerous other things that would pop-up, but I'm too lazy to type them all out.

Option 2
1. He does not use his attack command.
2. We have to set up some type of alternate move for every enemy in the game.
3. This can be exploited by the player.
4. This is assuming we have correctly modified the "make_action" method in Game_Enemy to correct for this.
5. Once again, I can think of about 10 other bufs that would arise, but I'm still too lazy.
Needless to say, you
ARE going to have bugs by making these "simple" mods. The problem is, although your mods may seem "simple", their actual implementation into the default CBS is not. They can all be done, but are going to require more than a line or two of code.
BTW:
Not introducing new methods does not make a script simpler.