1) deintergrate is not possible because the addon set and modifies registry settings in the image but you could try to integrate newer version in image contains older addon version, let me know if it's working
2) as bphlpt explained, .NET 3.5 Family is a completely separate package software than .NET 4.x Family
(2) Unlike in XP, earlier ".NET's" are now part of the OS, and are not designed to be removed, though I think they can be. And like XP, while .NET 4.5.1 completely replaces 4.5 and 4.0, it does not totally replace 3.5.1 and earlier in the sense that if you did remove 3.5.1 and earlier from your Win7 install, and a poorly written app looked specifically to see if 2.0 or 3.0 or 3.5 was installed, that app would fail even if you had 4.5.1 installed. At least that's the way I understand how things work.
For (1), I'll let abodi1406 or someone else that knows more than I do about this particular addon answer that definitively, but my opinion is that when you do a new build each month or whatever, and you have new hotfixes, addons, tweaks, etc., you are better off starting from scratch, rather than trying to remove the outdated ones and add the new ones in their place.
