Well I don't know if/how you could increase this but the chart already includes 15 pounds cargo and your rack is only rated to 10. I can tell you I'm 250 and 2 up we exceed the GVWR by about 20 with what I carry in the bags but I do just that. Carry a little more than 10 in each bag keeping the weight low and the light stuff on the rack.
I would think your concern would be more towards adjusting the pre-load on your shock prior to the ride for 2up loaded as your going to take it out and see how she rides and what your sag is. Calls for 3/4 -1 1/4" (see owners manual and need a friend to help) but I will tell you I run it a bit softer than that with no issues. I did bottom it out 1 time on a huge bump in the road I could not avoid and it was a solid thump but no issues other than that. As for handling, I had no issues in the twisties with a properly briefed passenger.
Not a technical answer but hope it helps.
2011 White Vision - Nuvi 550, Lowers, Lloydz 2nd filter, Vic perf filter, CB/Icom, 96 Brake LED's, Clear Signal lens/Switchbacks, VIC Hwy Pegs, Stebel Horn, 7Jurock 15" Shield, PCV, Lloyd ATS and Variable intake, Ness honkers
2004 V92 TC - S1 flash, level 1 slip-on, Ness big sucker K&N, ISO Grips, 4x1.5 Highway Hawg Risers, extra chrome (never too much), JM 2k CB 4' antena, Mustang seat, HD Front TS & Lowers, OD Pulley
Retired Navy SCPO