A couple of years ago I went with an Ohlins in my factory lowered 650 to bring it back to standard height and increase the load capacity for better two up riding. Only changes are the rear shock/spring and the kickstand. As has been said, nothing changes up front.
That said, shortly after changing the rear shock I became dissatisfied with the front suspension, particularly the dive and the front/back rocking of the bike over high speed bumps. I don't know if things actually changed because of the stiffer rear shock, or if the Ohlins was so good in the rear that it just made the shortcomings of the front suspension more obvious. In any case, a pair of intiminators had a very positive affect and I am happy with the suspension now.
2009 BMW F650GS
2007 Yamaha FJR1300A
2001 BMW R1150GS