I would definitely include anything that is optional, Doing otherwise could imply a lack of interest in the program.
If they do not specify the line spacing, I think that your interpretation is fair. I would recommend trying to make your case as succinct as possible though. From my understanding, adcoms appreciate brief but cogent SOPs more than their more verbose counterparts (as it shows writing aptitude and saves them time).
I would also recommend that you post your question in the "Faculty Perspectives" thread, as they would be able to provide much more insight as to whether or not something would get you "in trouble".