change chord symbols to reflect updated key

Nope, no better way.   This has been a gripe of mine for years also.  Changing keys is something that I end up doing quite often also, not always just for singers.  A Bb Trumpet player or any Sax has to xpose  chord changes on site if I have not had the time to create a lead sheet in Sibelius.  Fortunately, I work with players of the caliber where this is not a problem, so they bail me out quite often.
 
I love composing in Sonar 'cause it is easy to improvise and get good sounds and most likely because I am most familiar with it.  Notation programs are very clunky for composing unless you are strictly going measure by measure, note by note.  Even navigating is painful after you've worked in Sonar.
 
So here is my new trick,  seems to be OK so far.
 
1) Compose a melody on a dummy midi track in Sonar.
2) Export an XML of that track from staff view.
3) Rewire Notion and import the XML file.
4) Input Chords and Lyrics in Notion.
 
Now in this scenario I can transpose chords with no trouble.  I prefer to work notation in Sibelius, but it does not tag along Sonar as well as Notion does in rewire. Notion has other rewire sound issues, but I'm only using it for notation here.
 
The trouble i have is getting my head to work in different apps at the same time.  Sonar wants to do things a certain way and Notion wants to things other ways.  I'm trying to mitigate this issue by using a gaming keyboard that has extra macro keys.  I program the macros to do similar tasks in the different programs so I don't have to stop and think much about what I am doing.   
 
Hope that helps.....