I did a job for the MOD whilst being employed by a then large defence contractor,
MOD bods insisted on everything in their spec be just so. After looking at their spec for a while I thought you know what they won't want that, they will want this. So wrote the code to do both on the quiet. You could specify which it compiled by setting a SW switch on starting the compile.
A year later there was a collective suckling through teeth, amongst muttering of can't be done and going to cost from our team when the MOD bod changed their mind,
Got quite a bonus on that one.