Change default RRD graph definitions

Hello,

I'm looking to change the graph definitions for one of the built-in checks
e.g. [http].

The default creation method for the RRD graphs is "average", but I want to
display the "last" value instead.  The graphs.cfg file has this to create
http graphs:

[http]

DEF:p at RRDIDX@=@RRDFN@:sec:*AVERAGE*
LINE2:p at RRDIDX@#@COLOR@:@RRDPARAM@
GPRINT:p at RRDIDX@:AVERAGE: \: %5.1lf%s (avg)


What needs to be done to change the existing graphs on the system to
display *LAST* instead?


Thanks,
James