I have a list in Visual Studio 2010 with a custom forms (EditForm/NewForm). I deploy the project to SharePoint Server 2010, to update the New Item form.
The problem is that if I deploy the project then the list is updated and all the items are deleted. But I only want to update the New Item form (an application page).
If you have a content type for your list, you can update DisplayFormUrl, NewFormUrl and EditFormUrl:
var list = GetList();
var contentTypeId = GetContentTypeId();
var contentType = list.ContentTypes[contentTypeId];
contentType.NewFormUrl = "http://<servername>/newFormUrl.aspx";
I suppose you can move your aspx page used as form to separate feature or even a separate project (and separate WSP packet) - then you will be able to update this form alone.
You can simply copy-paste your page (.aspx) to server template folder (typically located here C:\Program Files\Common Files\microsoft shared\Web Server Extensions\14; where 14 - it's SharePoint 2010, 15 - SharePoint 2013) and execute iisreset.
If you've updated your code behind class: compile it and execute a gacutil command:
gacutil /i YourLibrary.dll
Also, you need execute an iisreset.
Hope, it's helpful for you.
