I see that Sprint web site allows changing the ESN online.

But - there is no mention of any cost or charge related to this
service, but after calling Sprint, no one really understood my
question and talked about upgrade, etc, and a $18 fee. And then the
$36 fee was also mentioned for certain activations.

So, has anyone recently done a ESN swap online, and if yes, did you
get a charge on your next bill or bills?

I need to do a temporary swap - change my account to a different ESN,
and then after two weeks, do another swap, so need to do two swaps
(have a damaged phone, old phone, and will soon have a new phone).

Any info on ESN swap cost for online swaps appreciated.