In reply to Managing kerning across weights in FontLab?:
Interpolate the new kern pairs for regular in a new file. Then replace the existing regular kerns with the new ones that you just interpolated. Unfortunately FontLab has problems with importing kerning, so it may be better and easier to split your final production fonts into individual files that import their kerning tables from OpenType feature files during compilation. That’s how I keep this stuff straight, but I’m also jumping between three other programs to do this stuff.
Read this thread for more on the subject: http://typophile.com/node/71250