If you view the event list for any given track, such as the drums, you can adjust individual events, and it will not affect the rest of them.
I do this all the time, for tweaking velocities on keyboard solos.
I should point out to you to be careful when using drum maps, because at this time Sonar has explicitly advised NOT to use drum maps on midi clips that were created using the Step Sequencer, as weird behavior DOES occur in that scenario.
If you have created a midi clip using Step Sequencer, and wish to edit it using a drum map, first bounce the Step Sequencer clips to a midi track, and that will make that particular issue go away.
Bob Bone