Windchaser

A bit of caution would be called for . I can see a temptation to make the cord "nice and tight".
Consider very carefully that ANY tension on the paracord from the rack down to the lower frame is in effect PRELOADING the seatpost rack by however many pounds/kilos pressure you pull on the cord MAGNIFIED by the lever arm length of the rack. Most of the paracord i'm familiar with is rated between 50 to 150 lbs. strength. Whereas most seatpost racks have load limits of 15 to 25 lbs.

TIGHTENING the PARACORD is the SAME as PUSHING down on the RACK. Reducing the amount of weight the rack can carry.