Any fields that are enabled, disabled or pre-populated should do so without having the page post back. What does this post back means?
postback (note it is one word) is a term used by ASP and JSF to describe a form which post to the same URL. It is Microsoft's way to pretend that variables on a web page can interact with each other like in event-driven desktop application, but I found it confusing because I know what really happens.
SO has great explanation.
For you it means that all widgets on the page should be enabled etc when page is first loaded, before clicking on submit button.
Online tranaction systems in general react to user demand. When the user requests something the request can either be satisfied by the users client device or by that device sending a request (a GET or POST normally) to the centralised servers.
A request to the servers will require activity on the network (to get the request to and the answer from the servers), plus time on the servers (in your example a trivial update).
So I imagine you are being asked in general not to initiate a server request for tivial changes.
If this relates to your organisations development standards then you must do your best to adhere to those standards. But be aware there will be times when trivial updates best serve the users needs or enhance security. So there is not a hard and fast rule for all.
Hope that helps and that I've understood your point but if not do get back and we'll do our best.