The question has two parts, one of which I already have the answer for.
I assume your questions is with regards to Java code. If that's the case, you don't actually need any extra plugins to accomplish 1). You can just go to Preferences -> Java -> Editor -> Save Actions and configure it to remove trailing whitespace.
By the sounds of it you also want to make this a team-wide setting, right? To make life easier and avoid having to remember setting it up every time you have a new workspace you can set the save action as a project specific preference that gets stored into your SCM along with the code.
In order to do that right-click on your project and go to Properties -> Java Editor -> Save Actions. From there you can enable project specific settings and configure it to remove trailing whitespace (among other useful things).
NB: This option has been removed in Eclipse Kepler (4.3) and following releases.
NB #2: The option seems to be back in Eclipse Luna - Luna Service Release 1a (4.4.1)
I would say AnyEdit too. It does not provide this specific functionalities. However, if you and your team use the AnyEdit features at each save actions, then when you open a file, it must not have any trailing whitespace.
So, if you modify this file, and if you add new trailing spaces, then during the save operation, AnyEdit will remove only these new spaces, as they are the only trailing spaces in this file.
If, for some reasons, you need to keep the trailing spaces on the lines that were not modified by you, then I have no answer for you, and I am not sure this kind of feature exists in any Eclipse plugin...
I am not aware of any solution for the second part of your question. The reason is that it is not clear how to define I changed. Changed when? Just between 2 saves or between commits... Basically - forget it.
I assume you would like to stick to some guideline, but do not touch the rest of the code. But the guideline should be used overall, and not for bites and pieces. So my suggestion is - change all the code to the guideline: it is once-off operation, but make sure that all your developers have the same plugin (AnyEdit) with the same settings for the project.
