UKP is a great tool for learning about other peoples experiences including all the bad practices that go on - time wasting, services not as advertised etc.,
Its probably possible to reflect back on lots of previous encounters and then realise, for instance, that the girl that you thought was being very friendly and chatty was actually just wasting your fun time, as an example. The more experiences that you have and the more you read UKP, then the more you learn to recognise all sorts of things.
I think to modify a review from a little while back would be wrong as that it what you genuinely thought at the time. Yes, writing reviews immediately after an encounter whilst still on high is probably not a good idea as others have said.
There is no harm in posting an addendum to your original review on the same thread on the lines of "thinking back guys ...etc.,"
I take all reviews no matter where they are as being subjective anyway. I am more interested in the basics - are the services, pictures accurate etc.,