Adding potentiometer to fixed SMPS circuit
No, you want to hook up the pot as a variable resistor, not a potentiometer to ground.  Remove the connection from the end of the variable resistor that you have going to ground, and hook that to the wiper of the variable resistor like this:


The way you have it drawn puts the &quot;bottom&quot; resistance of the pot in parallel with the lower feedback resistor, which will definitely cause unwanted behavior.