From a writable media you can just load to memory the part of Windows that you don't want to see modified and use the writable partition for your purposes.
yes, this is where IMDisk comes in the mix somehow but I have not explored it further.
also to me it seems EWF is better than FBWF from security standpoint since nothing is left writable on the partition but I think maybe the freeware alternatives mentioned would work better than both EWF and FBWF due to their limitations.
as to the legality of using M$ components beyond their intended usage, a brief study of contract law should enlighten one as to whether or not M$ has a valid contract with one whom uses EWF or FBWF. what are the requirements for a contract to be legally binding, and does M$ meet all these requirements?
I am not a lawyer (law merchant) I do not have a license to give legal advise so I dont say the correct answer but I think M$ will be changing to all subscription based service in the near future so that they can more properly control their code.
a legal study in licensing may prove beneficial to some in these (and many other) regards also. a law dictionary applicable to the political society one finds themselves involved in would be the best place to start. look up the definitions of these words, in many cases you will discover a new meaning for the words that you thought you already knew.
legalese is a different language that uses the same words except with different meanings. you may think you know what these words mean already but you probably do not.
"That depends on what the definition of is, is" - B. Clinton