If I understand your question correctly, you want to move the new slight modification of the drum pattern back and have it replace the pattern before it, right?
Or do you want them both?
In any event, the solution is similar.
Zoom in until you have both bars taking up most of the screen. Pick up the arrow tool and draw an outline that follows the outside of the bar you want to keep. The notes inside it sould turn dark as they are selected. Then use the 'control-G' command to group the notes. If you don't get the squared off bar but just some fraction of it try again until you get it to where it includes the space around the notes from the start and the end of the bar line.
This is known in Reason-speak as a group. It's only a one bar group but a group none the less. It should have a color, and if you repeat the process for other bars of a drum part they will have their own colors providing they differ slightly from the original.
This group can be copied and pasted like any other group using the control-c and control-v commands and combined with other drum groups to make a drum track.
