This was someone’s answer on a forum,not sure if it helps though but I’m posting it just in case
Well, I figured it out, so I thought I'd share the answer for the next time someone runs into this. It turned out to be the sequence of the steps that was the problem.
I was Adding the new User Preset, then setting the various settings the way I wanted them and then clicking Export. I assumed it would update the template and export the file, since there was no separate Save button. Wrong.
The correct, utterly counter-intuitive, sequence is to open the Export dialog, make all your desired settings, THEN click the Add button to create the new preset. You don't even have to click the Export button. Closing the Add Preset dialog after giving it a unique name causes LR to save the new preset.
So, there you go. I hope it helps someone.