I don't think making switching players slower will solve your issue, but rather exacerbate it instead. Any problem this fixes would only be replaced by a similar issue from the new interface as players may still be focused on one player when controlling another...
I haven't had this problem in a long time, but I remember when I was. I adjusted a few things in my game and haven't had the issue since. Maybe you'll have some success with some of these tips (assuming you're on PS3):
1) Switch by holding the O and moving the stick.
The analog controller holding O allows you to move to any player quickly, but requires you to master fine movement of the stick. It will be difficult to move the cursor to the player you want at first.
2) Switch by holding the O or X
When using the analog method to switch players, don't forget the old method still works. O switches one direction, while the X switches in reverse. If you pass the guy you want, just switch using the appropriate button.
3) Learn the Switch order
If you're using the method in #2, you'll need to be good at switching to the right guy. Each time you press O the cursor will begin on the D-Lineman on the left and cycle to the D-lineman on the right. It then moves to the linebacker on the left and cycles to the right. This is repeated for defensive backs and reversed for the X button. Remember, it's easy to pass players you want so you need to learn to use these buttons effectively...
4) Turn Player Lock "On"
In settings, turning player lock ON sets the cursor on the player you weere controlling at the beginning of the previous play. If you use the same player often, this makes switching pre-play less of an issue.
5) Learn all the positions
In those instances when you're caught on a guy you didn't want to control, having an understanding of your defensive call and knowledge of how to play each position is key. Resist the urge to move defenders immediately at the snap...
6) Adjust your play calls
Setting up defenses takes time. If you setup elaborate coverage disguises before switching to your desired defender, it's easy to get caught on the wrong guy. By calling plays that use assignments that are closest to the desired final defense you want to call reduces the time required to setup and select the proper defender.
Mind you, many of these adjustments will require you to put in time learning new things... But they work - especially when used in conjunction.
Hope this helps.
Later