@Noah *********
nope, you will not and IF you do take that 7 day stamp you're done and you can't change it to anything and you WILL have to leave.
You get documents from your school stating you stop studying on the date your extension runs out, you get documentation from your foundation saying you start the date the extension runs out, you go to the immigration office a week or so early cancel the ED extension and then immediately apply for a new extension based on volunteering.
I'd sure take someone from the foundation with you AND make sure they know you don't want to get a Non-O VISA, but only change the reason for your extension from education to volunteering.