Yup.. that's about the jist of it.. if you have 1.75 it's supposed to delete any unneccesary addons for you automatically... but if you're pre 1.75 you'll need to do it manually..
At the top of your mission.sqm file you'll find something that looks like this:
version=11;
class Mission
{
addOns[]=
{
"bis_resistance",
"bmp2",
"Su25",
"editorupdate102",
"BRDM"
just delete the addons that you're not using and then save.. you should be fine then ;D