yes, We’d need to know route (or flight/date). If I was a betting guy, I’d guess a non-PS, non-long haul HI domestic route. Am I right.

Unless I remember incorrectly, anything aside from PS or long haul HI (basically from DEN or east of there to HI), and the seats are not sold as PE - they are sold/services as E+, though the hard product is PE. So extra legroom and bigger screens, etc. As a result, these seats typically cost a bit more then the other E+ seats, or if elite, are selectable for free based on the window (check in for silver, time of booking for gold and above).

assuming these are sold as regular E+, the deal is the same as other E+. Your purchase is for a specific seat - the amounts can and do vary by seat and demand. If you want to change your seat, the deal is you have to pay full price for the new one, and by default, when the aircraft departs, you’ll be given a refund for your original seat purchase. Some reports have said that those purchasing new E+ seats have filed for a refund prior to departure on the website received it, though that’s not the ‘official’ process - officially, it will be refunded after departure - it takes about a week after that to show up on your statement. An agent may be willing to allow you just to pay the difference, but again, that’s not SOP, so they may deny that.

honestly, if it were me, I’d just select the new seat, pay for it, and either wait for a week after departure for standard refund, or file a refund request online if you’d rather not wait. No point really in waiting for an agent, IME, for something that might/might not be done.