Fetch all set feeds (verify if set). Then output them as parameters at the start of an operation or tool change. Use the motion parameters to output the right parameter number after each move if it is changed. Obviously some of the formats need to change for instance you will need to output in string format or use a special field e.g. with a leader that looks like F=#. How you implement it depends upon your own taste. It is fun to program takes some time to get it right. Most of my postprocessors use parametric feeds as a standard feature. Even inverse feeds are included then I use formulas e.g. F=0.55*#123.