Export your kerning to an OpenType feature file. Load the font into Metrics Machine and then import the kerning from the feature file. Scale all of your kerning values to match the letter scaling, export that as a feature file, and then copy/paste it into an OpenType feature in Fontlab.

1. Edit your old.fea file (leave only new kern feature):

# deleted
lookup kernHorizontalKerninglookup1 {
subtable;
@kc36_first_0 = [\a \uni1EB7 ];
# etc
@kc36_second_1 = [\b ];
# etc

pos @kc36_first_0 @kc36_second_1 -8; # -8 is new kern value
# etc, the rest of kern values

subtable;

} kernHorizontalKerninglookup1;

feature kern {

script DFLT;
language dflt ;
lookup kernHorizontalKerninglookup1;

# etc, the rest script/language registrations
} kern;

2. Save edited file: new.fea
3. Delete kerning in FontInfo

Thanks @Dunwich type (I do not have Fontlab but I appreciate the help).
Thanks @JanekZ: This is tremendously helpful. I tried exactly that (updating the fea file automatically in Open Office Calc) but without having deleted the original kern table so the "Merge Feature Info" bit did not appear. I'll try this when back at home tonight. Thanks muchly.

PS. Am v jalous of how clean your fontforge looks!

It is fontforge-mingw_2010_05_18 without any modifications on winXP. No fancy gadgets ;)
Be very careful with your new.fea file, any error will crash FF without warning (and error report).

Success! Thanks. I have not been able to find a 2010 version of fontforge for cygwin on Vista. I must try harder...