You can lighten the 617 trigger without compromising ignition by replacing the rebound slide spring.
This spring (among other functions) powers the trigger.
This has no effect on the main spring, which powers the hammer, which is what determines ignition.
As above, good money, well spent for a S&W owner is a copy of the Kuhnhausen manual.
This is a real pistolsmiths manual on the S&W, and gives explicit details on spring replacement and action tuning without ignition problems.
MidwayUSA - "The S&W Revolver: A Shop Manual" Book by Jerry Kuhnhausen
For lighter spring kits, check Brownell's and Midway for "K" frame rebound springs. Due to some problems with .22 "K" frame ignition, stick with the factory original mainspring.