hy sierevello
if you alter the feed, then be sure that once the tap reaches the bottom, you won't ruin your toolholder, but still have room available; thus do the math, calculate how much your toolholder will extend, and check if it is actually capable of doing it, but don't go over 80%eq, thus don't use it at the limit
also, a major factor is how your cnc syncronizes spindle phase and z travel, how much lag is there before reversing, etc ... to reduce all these unknows, use a lower rpm, since higher rpms require more reaction time / kindly
ps : you said that there is no cycle for rigid tapping, but maybe there is for float tapping ?